CH 2230 Final Exam
D. an ionic bond (Potassium is a Group 1 metal, and oxygen is a Group 6 nonmetal. Bonds formed between metals and nonmetals are mostly ionic.)
A bond formed between potassium and oxygen is best described as: A. a nonpolar covalent bond B. a polar covalent bond C. an atomic bond D. an ionic bond
C. two; four (Diastereomers are compounds that have more than one chiral carbon where the spin of at least one of them is identical and one of them is opposite; i.e. (R,R) vs. (R,S). Both A and B can be ruled out for only having one chiral carbon, and D can be ruled out because only four possibilities exist: (R,R) vs. (R,S), (R,R) vs. (S,R), (S,S) vs. (R,S), and (S,S) vs. (S,R).)
A molecule that has ______ chiral carbon(s) will have ______ pair(s) of diastereomers. A. one; one B. one; two C. two; four D. two; six
C. 16 (The number of stereoisomers is determined by using the formula 2n, where n is equal to the number of chiral carbons (24 = 16 stereoisomers).)
A molecule with four chiral carbons will have a total of ________ stereoisomers. A. 4 B. 8 C. 16 D. 32
D. 4 (When determining the degrees of unsaturation, halides count as hydrogen atoms while each nitrogen atom takes one hydrogen atom away. In this formula, this net change would make 18 hydrogen atoms. The saturated formula would have 26 hydrogen atoms (2n + 2) and half of the difference gives four degrees of unsaturation.)
Fenfluramine is an appetite supressant with the chemical formula C12H16F3N. How many degrees of unsaturation does the structure have? A. 7 B. 6 C. 5 D. 4
A. 6 (1° hydrogen atoms are characterized as such because they are bonded to 1° carbons, and 1° carbons are those carbons that are bonded to only one other carbon. The molecule shown has eight (6 from the two methyl groups, and 2 from the end of the alkene).)
How many 1º hydrogen atoms are in the following molecule? A. 6 B. 7 C. 8 D. 9
D. 4 (A chiral carbon is one that is bonded to four different groups; the molecule shown has four:)
How many chiral carbons are in the molecule below? A. 1 B. 2 C. 3 D. 4
B. 5 (Constitutional isomers are different molecules that have the same molecular formula. C6H14 is a saturated formula, and five different structures can be drawn: hexane, 2-methylpentane, 3- methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane)
How many constitutional isomers have the formula C6H14? A. 4 B. 5 C. 6 D. 7
D (Geminal is from the Latin gemini, meaning "twins". It is a descriptor used in Organic chemistry when two functional groups are bonded to the same carbon. A is a 1,4-dihalide, C is a 1,3-dihalide, and B is a 1,2-dihalide (vicinal, from Latin vicinus, or "neighbors").)
Which of the following is an example of a geminal dihalide?
C (Alcohols are classified according to the carbon they are bonded to. An allylic alcohol then is a molecule that contains an alcohol bonded to an allylic carbon.)
Which of the following is an example of an allylic alcohol?
B. NH3 (A Lewis acid is an electron acceptor, and nitrogen in B already has a filled octet. While this is also true of the oxygen in A, H3O+ refers to H+ , and a proton is perhaps the most common Lewis acid.)
Which of the following is not a Lewis acid? A. H3O+ B. NH3 C. BH3 D. AlBr3
A. regioselective (The question itself is the "textbook" definition of a regioselective reaction. Addition reactions that follow Markovnikov's rule (more stable cation) and elimination reactions that follow Zaitsev's rule (more stable alkene) are examples of regioselective reactions.)
A reaction in which a mixture of two constitutional isomers is obtained but more of one is formed than of the other is called A. regioselective B. regiospecific C. stereospecific D. stereoselective
A. Addition of the electrophile to the less substituted carbon (The first step in an alkene addition reaction that follows Markovnikov's rule involves two π-electrons from the alkene reacting as a nucleophile to form a new bond to an electrophile. The electrophile will bond to the less substituted carbon so the cation forms on the more substituted carbon. The nucleophile will add to the more substituted carbon in the second step.)
According to Markovnikov's rule, what is the first step in an addition reaction to an alkene? A. Addition of the electrophile to the less substituted carbon B. Addition of the electrophile to the more substituted carbon C. Addition of the nucleophile to the less substituted carbon D. Addition of the nucleophile to the more substituted carbon
B. It will be the most substituted alkene (Zaitsev's rule is to elimination reactions as Markovnikov's rule is to addition reactions. A reaction that follows Zaitsev's rule will form the most substituted alkene. This alkene may or may not be the most stable since (Z)-alkenes can form in an E2 reaction depending on where the β-hydrogen is (see Question #32).)
According to Zaitsev's rule, what will be true regarding the identity of the major product in an elimination reaction with a small base? A. It will be the most stable alkene B. It will be the most substituted alkene C. It will be the least stable alkene D. It will be the least substituted alkene
A. a quaternary ammonium salt (A quaternary ammonium salt has a nitrogen atom bonded to four carbons, thus the positive charge on nitrogen (ammonium). Because it is a salt, it would be a solid.)
Assuming roughly equivalent molecular weights, which of the following compounds has the highest boiling point? A. a quaternary ammonium salt B. a 1º alcohol C. a 3º alkyl chloride D. a 1º amine
B. 5 (Constitutional isomers are compounds that have the same formula but are put together differently. Given the formula, the first structure would likely be cyclopentane. The remaining structures can be drawn by dropping a carbon from the parent and bonding a methyl group to cyclobutane, two methyl groups to cyclopropane, or an ethyl group to cyclopropane:)
How many constitutional isomers with one ring have the chemical formula C5H10? A. 4 B. 5 C. 6 D. 7
D. 3 (To fulfill their respective octets, nitrogen has one lone pair of nonbonded electrons and oxygen has two.)
How many nonbonding pairs of electrons are in H2NOH? A. 0 B. 1 C. 2 D. 3
C. 5 (See Question #41. In the first step, two π-electrons from the alkyne form a new bond between the terminal carbon and a hydrogen atom from the acid. This generates a 2° vinyl cation. Water attacks the cation in Step 2, and the acid catalyst is recycled in Step 3 to form a neutral vinyl alcohol. This rearranges under acidic conditions. Oxygen forms a double bond to the carbon it is bonded to in Step 4, and water neutralizes the ketone in Step 5.)
How many steps are required in the mechanism of the following reaction? A. 3 B. 4 C. 5 D. 6
B. 8 ( This molecule has three chiral carbons so eight stereoisomers can be drawn. The middle carbon is not chiral since it is bonded to three identical groups (sec-butyl):)
How many stereoisomers can be drawn for the following molecule? A. 16 B. 8 C. 4 D. 2
C. 2 (The electronic configuration for carbon is 1s2/2s2/2p2, and both electrons in the 2p orbital are unpaired)
How many unpaired electrons are present in the electronic configuration of carbon? A. 0 B. 1 C. 2 D. 3
D. 9 (The carbon atoms in an alkyl halide can be characterized by where they are in relation to the halide. The carbon bonded to the bromine is an α-Carbon, and each successive carbon is labeled using the Greek alphabet:)
How many γ-hydrogens does the following molecule have? A. 1 B. 3 C. 6 D. 9
D. 13 (All single bonds are σ-bonds, and double or triple bonds also contain one σ-bond. It may be useful to draw the Lewis structure to count all of the carbon-hydrogen bonds:)
How many σ-bonds are in the following molecule? A. 4 B. 8 C. 12 D. 13
D. a 2º halide and a methyl alcohol (The alcohol is bonded to a carbon that is not bonded to any other carbons (methyl), and the halide is bonded to a 2° carbon (a 2° halide).)
In addition to the ether, what functional groups are present in the following molecule? A. a 3º halide and a 1º alcohol B. a 2º halide and a 1º alcohol C. a 3º halide and a methyl alcohol D. a 2º halide and a methyl alcohol
C. SN2 (The intermediate formed in this mechanistic step is called a transition state, where one bond is trying to form at the same time another one is trying to break. This occurs in an SN2 reaction, where the nucleophile attacks the carbon from the side opposite the leaving group (i.e. backside attack).)
In which type of reaction does the following mechanistic step occur? A. E1 B. E2 C. SN2 D. SN1
A. (2S,3R) (. The spin around Carbon #2 is initially clockwise, and the spin around Carbon #3 is initially counterclockwise. Since each hydrogen has a wedge bond, both spins are flipped.)
Indicate the correct stereochemical configuration for the molecule below. A. (2S,3R) B. (2S,3S) C. (2R,3R) D. (2R,3S)
D. (2R,4S) (The molecule would be numbered to make the alcohol bonded to Carbon #2. The priorities of the groups bonded to Carbon #2 are numbered in black, and those bonded to Carbon #4 are numbered in red:)
Indicate the correct stereochemical configuration for the molecule below. A. (2S,4S) B. (2R,4R) C. (2S,4R) D. (2R,4S)
B. (3R,4R) (The alcohol in this structure gets naming priority, and since the amine becomes an amino substituent, the carbon chain is numbered beginning with the alkene. Carbon #3 and Carbon #4 are both chiral, and the spins can be determined the usual way. The priorities of the groups bonded to Carbon #3 are shown in blue, and those bonded to Carbon #4 are shown in red:)
Indicate the correct stereochemical configuration for the following molecule. A. (3R,4S) B. (3R,4R) C. (3S,4R) D. (3S,4S)
B. (1R,2S) (This structure has only two carbons, and the back carbon is Carbon #1 since chloro comes before fluoro alphabetically. The priorities of the groups bonded to Carbon #1 are (1) chlorine, (2) oxygen, (3) Carbon #1, and (4) hydrogen. Bonded to Carbon #2 are (1) fluorine, (2) oxygen, (3) Carbon #1, and (4) hydrogen)
Indicate the correct stereochemical configuration for the following molecule. A. (1R,2R) B. (1R,2S) C. (1S,2S) D. (1S,2R)
C. 46 (An acyclic structure is one that does not have a ring, and the alkene counts as one degree of unsaturation. A completely saturated molecule with 23 carbon atoms would have 48 hydrogen atoms. With one degree of unsaturation, the formula would then have 46 hydrogen atoms.)
Muscalure is an acyclic alkene that contains 23 carbon atoms. How many hydrogen atoms does it have? A. 23 B. 44 C. 46 D. 48
A. It can have six π-bonds (A bicyclic molecule is one that has two rings in its structure. A saturated molecule with 14 carbon atoms would have 30 hydrogen atoms (2n + 2), and this formula only has 14. This leads to a structure with 8 degrees of unsaturation (30 - 14 = 16; 16 ÷ 2 = 8). Because the structure has two rings, the other six degrees can come from six π-bonds.)
Naproxen is a bicyclic molecule with a chemical formula of C14H14O3. Which of the following could be true regarding its structure? A. It can have six π-bonds B. It can have eight π-bonds C. It can have four rings D. It can have four triple bonds
B. HF; HI (Bond strength increases as bond length decreases, and bond length increases as atomic size increases. Therefore the shortest and strongest bond is in HF, while the longest and weakest bond is in HI.)
Of the hydrogen halides, the strongest bond is found in ________ and the longest bond is found in ________. A. HF; HF B. HF; HI C. HI; HF D. HI; HI
B. substitution; alcohol (Alkyl halides react with water in substitution reactions, and the product formed is an alcohol. The reaction shown is an example of an SN1 reaction.)
The conditions of the following reaction will favor _______, and the major product will be an _________. A. elimination; alkene B. substitution; alcohol C. addition; alcohol D. no reaction; alkyl halide
B. 5 (The number of stereoisomers that can be drawn can be determined using the formula 2n, where n is the number of chiral carbons. If 32 stereoisomers can be drawn, n is equal to 5 (25 = 32).)
Thirty-two stereoisomers of Glucose can be drawn. How many chiral carbons does glucose have? A. 4 B. 5 C. 8 D. 16
A. (Z)-3,4-dimethyl-2-hexene (Hydrogenation is an addition reaction that reduces π-bonds to alkanes. The amount of energy given off by the reaction corresponds to the stability of the alkene. Alkene stability is generally simplified as "more substituted = more stable", and (E)-alkenes are more stable than (Z)-alkenes. Since A is the least stable of the four alkenes, it will have the highest potential energy and will therefore release)
Upon hydrogenation, which of the following alkenes releases the most amount of energy? A. (Z)-3,4-dimethyl-2-hexene B. (E)-3,4-dimethyl-2-hexene C. (Z)-3,4-dimethyl-3-hexene D. (E)-3,4-dimethyl-3-hexene
A. [CH3S]- (The methoxide anion is the base in the reactants and a proton bonded to sulfur is more acidic than one bonded to carbon. Therefore, the anion takes the proton from sulfur to form methanol and a sulfur anion)
What base is formed in the following acid-base reaction? A. [CH3S]- B. [CH3SH2]+ C. CH3OH D. [CH2O]-
D. 2º vinyl cation (The "acid-catalyzed hydration of a terminal alkyne" is the reaction where water is added to an alkyne using an acid catalyst (see Question #42). The final product is a ketone (scratch A). An aldehyde is the final product using hydroboration / oxidation conditions (scratch B). A 2° cation is formed in the reaction, but since the carbon it forms on is part of a double bond (a vinyl carbon), the best answer is D.)
What intermediate forms in the acid-catalyzed hydration of a terminal alkyne? A. ketone B. aldehyde C. 2º cation D. 2º vinyl cation
D (This step shows the formation of a new bond between the negatively charged carbon and the carbon on the other end of the molecule double bonded to oxygen (5 atoms in between). The second arrow shows the double bond between the carbon and oxygen breaking to form a lone pair of electrons on oxygen making it negatively charged. )
What intermediate product would be formed as a result of the following mechanistic step?
D. isobutane (The compound contains four carbons overall (butane) and a branch (the iso-structural unit). Therefore the common name is isobutane.)
What is the common name of the following compound? A. isopropylmethane B. tert-butane C. isopropane D. isobutane
A. [CH3NH]- (A conjugate base is formed when an acid loses its proton and gains a negative charge. Protons bonded to nitrogen are more acidic than those bonded to carbon)
What is the conjugate base of CH3NH2? A. [CH3NH]- B. [CH2NH2]- C. [CH3NH3]+ D. [NH2]
C. sp2 (The compound shown is an alcohol, and the carbon chain is numbered so the alcohol is bonded to Carbon #3. Compounds containing both alkene and alkyne functional groups are numbered so that both get the lowest numbers they can have. In the case of a tie, the lower number goes to the alkene ('e' comes before 'y' alphabetically). Carbon #1 is sp2 hybridized since it has three regions of electrons around it:)
What is the hybridization of Carbon #1 in the following structure? A. p B. sp3 C. sp2 D. sp
B (The conditions for this reaction promote an E2 pathway (strong base, protic solvent, heat). An E2 reaction is stereospecific, meaning the stereochemistry in the product will depend on the stereochemistry in the reactant. In order for the reaction to proceed, the β-hydrogen needs to be anti to the leaving group. This means the back carbon will need to be rotated counter-clockwise 60°. The two methyl groups are both pointing up and the two ethyl groups are both pointing down. After the reaction, both of these relationships are maintained, resulting in the (Z)-alkene:)
What is the major product in the following reaction?
C (The reaction shown is an example of an acid / base reaction, but with the reactants serving as Lewis acids and bases. Sulfur (the Lewis base) uses one of its lone pairs of electrons to form a new bond with boron (the Lewis acid) to form the salt as a product.)
What is the major product in the following reaction?
A (The reaction shown is an addition reaction, and HBr adds to alkenes in the presence of H2O2 to form an alkyl halide (anti-Markovnikov). No rearrangements occur with radicals)
What is the major product of the following reaction?
A (The reaction shown will favor an E2 pathway (strong base, protic solvent, heat). The β-hydrogen in an E2 reaction needs to be anti- to the leaving group, so in this case, the less substituted alkene is formed.)
What is the major product of the following reaction?
B (The reaction shown is an addition reaction, and HBr adds to alkenes to form alkyl halides. The reaction follows Markovnikov's rule, and the stereochemistry in the product is racemic due to the formation of a cation intermediate.)
What is the major product of the following reaction?
C (The reaction shown is an addition reaction, and Br2 adds to alkenes with H2O as a solvent to form a halohydrin. The reaction follows Markovnikov's rule (Br is the electrophile). The stereochemistry in the product results from an anti-addition, but when only one chiral carbon is formed, it becomes racemic.)
What is the major product of the following reaction?
A. C8H12 (A completely saturated hydrocarbon (only carbons and hydrogens) with 8 carbon atoms would have a formula of C8H18. With three degrees of unsaturation, six hydrogen atoms are missing to give a formula of C8H12.)
What is the molecular formula of a hydrocarbon that contains 8 carbon atoms, one ring, and two π bonds? A. C8H12 B. C8H12O C. C8H14 D. C8H14O
D (The reaction shown is an addition reaction, where m-CPBA adds to an alkene to form the epoxide (A or D). In the product, the isopropyl group and the ethyl group have opposite bonds. In order to get this stereochemistry, the (E)-alkene is required (a syn-addition).)
What starting material should be used to produce the major product shown in the following reaction?
A. Constitutional isomers (Neither structure has a chiral carbon, even though both are drawn with stereochemical bonds. The first structure is 2-chloropropane, and the second one is 1-chloropropane. They are only different by how they are put together (constitutional isomers).)
What is the relationship between the following pair of molecules? A. Constitutional isomers B. Conformational isomers C. Enantiomers D. Identical compounds
C. identical compounds (Both molecules have the same formula and the same functional groups, and the functional groups are all bonded in the same places (scratch A). Only one chiral carbon is present (scratch D). The difference between B and C comes down to the spin. Since both molecules have the same spin (S), they are identical compounds.)
What is the relationship between the following pair of molecules? A. constitutional isomers B. enantiomers C. identical compounds D. diastereomer
D. diastereomers (The base name for these structures is 2-chlorobutane-2,3-diol. The stereochemistry for both chiral carbons needs to be determined and compared. The first structure is (2S,3R) and the second is (2R,3R); therefore, these are diastereomers.)
What is the relationship between the following pair of molecules? A. constitutional isomers B. enantiomers C. identical compounds D. diastereomers
C. identical compounds (The molecules appear to be mirror images, but the bonds at the two chiral carbons have been inverted. Drawing a mirror image and flipping the bonds results in the formation of the same molecule. Alternatively, the spins can be determined - both are (4S,6R).)
What is the relationship between the pair of molecules shown below? A. meso compounds B. enantiomers C. identical compounds D. diastereomers
D. diastereomers (The carbon chain can be numbered from left to right. The stereochemistry in the first molecule is (2S,3S) and that of the second molecule is (2R,3S). With one spin identical and the other opposite, the molecules are diastereomers.)
What is the relationship between the pair of molecules shown below? A. meso compounds B. enantiomers C. identical compounds D. diastereomers
B. (E)-2-(2-aminoethyl)pent-1-en-1-ol (The alcohol gets naming priority over the amine, and the longest carbon chain is numbered. The fivecarbon chain has an ethyl group bonded, and this ethyl group as an amino group bonded to its second carbon. The alcohol and the ethylamino substituent are on opposite sides of the alkene to give (E).)
What is the systematic name of the following molecule? A. (E)-4-amino-2-propylpent-1-en-1-ol B. (E)-2-(2-aminoethyl)pent-1-en-1-ol C. (Z)-2-(2-aminoethyl)pent-1-en-1-ol D. (Z)-4-amino-2-propylpent-1-en-1-ol
D. (S)-cyclohex-2-en-1,2-diol (Both alcohols get priority over the alkene, and an alkene needs to be numbered consecutively (2-en1,2-diol). The initial spin of the chiral carbon is clockwise, but since the hydrogen has a wedge bond, it needs to be flipped.)
What is the systematic name of the following molecule? A. (R)-cyclohex-1-en-1,2-diol B. (S)-cyclohex-1-en-1,2-diol C. (R)-cyclohex-2-en-1,2-diol D. (S)-cyclohex-2-en-1,2-diol
A. (S)-3-(aminomethyl)-5-methylhex-1-en-3-ol (The alcohol in this structure gets naming priority, and it is bonded to a carbon atom in a chain of six carbons. The amino group is bonded to a carbon that is bonded to the parent chain (aminomethyl). The lowest priority group bonded to the chiral carbon is already in the back, giving an S-spin.)
What is the systematic name of the following molecule? A. (S)-3-(aminomethyl)-5-methylhex-1-en-3-ol B. (R)-3-(aminomethyl)-5-methylhex-1-en-3-ol C. (S)-1-amino-4-methyl-2-vinylpentan-2-ol D. (R)-1-amino-4-methyl-2-vinylpentan-2-ol
C. (E)-hexa-1,3-dien-5-yne-3,4-diamine ()
What is the systematic name of the following molecule? A. (Z)-hexa-1,3-dien-5-yne-3,4-diamine B. (E)-hex-1-yne-3,5-dien-3,4-diamine C. (E)-hexa-1,3-dien-5-yne-3,4-diamine D. (Z)-hex-1-yne-3,5-dien-3,4-diamine
D. 1-isopropoxy-2-methylpropane (The molecule is named systematically (IUPAC) so that the parent chain is bonded to the most substituents:)
What is the systematic name of the following molecule? A. isobutyl isopropyl ether B. 1-isobutoxy-1-methylethane C. 2-isobutoxypropane D. 1-isopropoxy-2-methylpropane
C. π (The atomic orbitals shown are p-orbitals, and when they overlap vertically, they form π-molecular orbitals. If the shaded end of one of the orbitals overlaps with the unshaded end of the other, then a π*-molecular orbital is formed (an anti-bonding orbital).)
What kind of molecular orbital results when the two atomic orbitals shown below are combined? A. σ B. σ* C. π D. π*
A (This step begins with a lone pair of electrons on the oxygen. The first arrow indicates the formation of a carbon-oxygen double bond (scratch B). The second arrow indicates the formation of a carbonhydrogen bond using two π-electrons from the alkene (scratch D). The third arrow shows an oxygenhydrogen bond breaking, and the two electrons that made the bond ending up on oxygen as a lone pair (scratch C).)
What products would form as a result of the following mechanistic step?
C (The reaction shows an alkene formed from an alkyl halide, and this will occur if the reagents used favor elimination (A or C). The alkyl halide is 1º, so the pathway needs to be E2 (strong base, protic solvent, heat).)
What reaction conditions should be used to form the product shown as the major product?
C (The reaction shows the formation of an alcohol from an alkene, and this is achieved by an addition reaction. Because the 1º alcohol is formed, hydroboration / oxidation is required (anti-Markovnikov).)
What reaction conditions should be used to form the product shown as the major product?
D (The product of this reaction is an ether, and the acid catalyst under the reaction arrow indicates it is formed by an addition reaction (scratch A). B, C, and D will all form an ether, but the stereochemistry in B will be racemic, and the enantiomer would form in C.)
What starting materials would be necessary to form the major product shown in the highest yield?
B. a protonated ether and a 1º amine (A 2º alcohol is an OH group bonded to a 2º carbon, and this is not present in this structure (eliminating A and C). Amines are classified by how many carbons the nitrogen is bonded to. In this structure, nitrogen is only bonded to one carbon, making it a 1º amine)
What two functional groups are present in the following molecule? A. a 2º alcohol and a 1º amine B. a protonated ether and a 1º amine C. a 2º alcohol and a 3º amine D. a protonated ether and a 3º amine
A. A (Z)-alkene (Hydrogenation can occur with either alkenes or alkynes, and any stereochemistry formed results from a syn-addition. The product has wedge bonds to bromine and chlorine. Therefore, they would need to be on the same side of the double bond in the starting material (a (Z)-alkene). The cis prefix can only be used when two different groups are bonded to the alkene.)
What type of starting material would be needed to form the product shown as the major product? A. A (Z)-alkene B. An (E)-alkene C. A cis-alkene D. A trans-alkene
A. ether; CH3(CH2)4CO2H (A solution with a pH = 3 is acidic and is slightly more acidic than the carboxylic acid. This means the acid will exist primarily in its acidic form (the solution donates a proton). Long chain carboxylic acids (more than 4 carbons) that are neutral are insoluble in water)
When a small amount of CH3(CH2)4CO2H, (pKa ~ 4.8) is added to a separatory funnel that contains ether and water with a pH = 3.0, it is found mainly in the ________ layer as ________. A. ether; CH3(CH2)4CO2H B. water; CH3(CH2)4CO2H C. ether; CH3(CH2)4CO2- D. water; CH3(CH2)4CO2-
D (The base name of this molecule is 1,2-diethyl-3-methylcyclohexane. When a ring flips, groups that were originally axial will become equatorial, and groups that were originally equatorial will become axial. Their spatial arrangement does not change. In this structure, all three substituents are pointing up (above the ring). When the ring flips, all three substituents will still be pointing up (scratch A, B, and C). B has the substituents bonded correctly, but since all are all pointing down, B and D would be enantiomers. Only D is identical to the starting structure.)
Which conformation would result if the following chair structure undergoes a ring flip?
D (The most stable chair conformation is (1) the one with the most groups in equatorial positions or (2) the one with the larger groups in equatorial positions. B can be ruled out because it is a different compound altogether. A has all four groups equatorial, but the alcohols and their adjacent methyl groups are pointing opposite directions. C can be ruled out since methyl groups are larger than alcohols)
Which is the most stable chair conformation of the following substituted cyclohexane?
B (Potassium methoxide is an ionic compound and a strong base (KOCH3), and pairing it with an aprotic solvent such as DMF will favor an SN2 reaction. The reactivity order for an SN2 reaction is 1º > 2º >> 3º, and both A and B have a 1º halide. The difference between the two is the position of the methyl branch on the parent chain. The nucleophile has to approach the electrophile from the back side, and the farther away the methyl group is, the less likely it is to interfere with the reaction.)
Which of the following alkyl halides would react the fastest with potassium methoxide in dimethylformamide (DMF)?
C. the C-N-C bond in a quaternary amine (The C-O-C bond angle in an ether and a 3º alcohol is ~ 104.5 due to the tetrahedral geometry and two lone pairs of electrons. The C-N-C bond angle in a 2º amine is ~ 107.5 due to the tetrahedral geometry and one lone pair of electrons. The C-N-C bond angle in a 4º amine is 109.5 due to the tetrahedral geometry and no lone pairs of electrons.)
Which of the following has the largest bond angle? A. the C-O-C bond in an ether B. the C-N-C bond in a secondary amine C. the C-N-C bond in a quaternary amine D. the C-O-C bond in a tertiary alcohol
A. (All four molecules are hydrocarbons, so the boiling point depends on Van der Waals forces. These forces decrease as branching in the molecule increases, so A has the lowest boiling point of the four.)
Which of the following has the lowest boiling point?
B (Sulfur is in Group 6, so it can form two bonds when neutral. It will then have two lone pair electrons to fulfill its octet.)
Which of the following has two lone pairs of electrons on the central atom? A. CO2 B. SCl2 C. NF3 D. H3O+
A (Like hydrogen atoms and alcohols, halides are characterized by the type of carbon they are bonded to. A vinyl halide is a halide that is bonded to a vinyl carbon, and a vinyl carbon is one that has a double bond to another carbon)
Which of the following is an example of a 2º vinyl halide?
A (A nucleophile is defined as a negatively charged anion or a partially negative atom with a lone pair of electrons. B and C can be ruled out since both phosphorous and nitrogen are more electronegative than hydrogen, and they each have a lone pair of electrons. D can be ruled out since sulfur is more electronegative than hydrogen, and it has two lone pairs of electrons. Because boron is in Group 3, it will form three bonds, which gives it an incomplete octet. Because of this, BH3 is an electrophile.)
Which of the following is not a nucleophile? A. BH3 B. PH3 C. NH3 D. SH
D. -Br (An aqueous solution is classified as a protic solvent. Protic solvents are capable of solvating smaller nucleophiles, so nucleophilicity increases with increasing atomic size.)
Which of the following is the best nucleophile in an aqueous solution? A. F- B. -OH C. -NH2 D. -Br
C. -NH2 (Hexane is an aprotic solvent, and in such solvents nucleophilicity increases along with base strength (stronger bases are better nucleophiles). Of the choices, − NH2 is the strongest base, making it the best nucleophile.)
Which of the following is the best nucleophile in hexane? A. F- B. -OH C. -NH2 D. -Br
D. [CH3OH2]+ (The pKa value of neutral amines is ~35, of neutral alcohols is ~15, of protonated amines is ~10, and of protonated alcohols is > 0. The lower the pKa value, the stronger the acid.)
Which of the following is the strongest acid? A. CH3NH2 B. [CH3NH3]+ C. CH3OH D. [CH3OH2]+
A (The reaction shown is a substitution reaction, and because methanol is a weak base, an SN1 pathway is favored: The leaving group is lost in Step 1 (B), a hydride shift occurs in Step 2 (D), and the methanol attacks the cation in Step 3 (C). The final step needs to show a nucleophile taking the extra proton away.)
Which of the following mechanistic steps would not be valid in the following reaction?
C (The reaction shown is an addition reaction, where the less substituted alkyl halide is formed due to the presence of H2O2 (see Question #39). The reaction proceeds through radical intermediates where (B) is Step 1, (D) is Step 3, and (A) is Step 4. The step shown in (C) does not occur.)
Which of the following mechanistic steps would not be valid in the following reaction?
B (An allyl functional group contains a terminal alkene and is composed of three carbon atoms. It is only a functional group if it is not part of the parent chain)
Which of the following molecules contains an allyl functional group?
B. II (III does not have any chiral carbons, so it can be ruled out. Both I and II have two chiral carbons, but I is a meso compound. Meso compounds have chiral carbons, but their rotations cancel each other out, making the molecule achiral overall.)
Which of the following molecules is chiral? A. I B. II C. III D. All three are chiral
D (A carbocation rearrangement can occur anytime a 2° cation forms and an adjacent carbon is either (1) 3° and bonded to a hydrogen, (2) 4° and bonded to a methyl group, or (3) part of a cyclobutane ring. When chloride leaves in D, a 3° cation is generated, so any kind of shift is unnecessary.)
Which of the following reactants would not undergo a carbocation rearrangement in an SN1 reaction?
A (Elimination reactions using small bases will follow Zaitsev's rule (scratch D). A, B, and C will all form the less-substituted 1-butene, but the reactivity order in an E2 reaction is 3° > 2° > 1°. The 2° halide in A will react faster than the 1° halide in B and C.)
Which of the following reactions would form 1- butene in the highest yield?
c (The most stable chair conformation will have (a) more substituents equatorial or (b) the largest substituent equatorial. The cis- prefix in the name means the two substituents are bonded on the same side of the ring, and their 1,3-substitution pattern means the most stable conformation will be the one where both are equatorial.)
Which of the following represents the most stable conformation of cis-1-bromo-3- methylcyclohexane?
B (In the original structure, the two ethyl groups are axial while the two methyl groups are equatorial. Three of the four substituents are pointing down. When the ring flips, the groups that were bonded axial will end up bonding equatorial (and vice versa))
Which of the following represents the ring flipped structure of the compound shown below?
B (The molecule shown in the Newman projection is (2S,3R)-2,3-dibromo-3,4-dimethylpentane. Converting a Newman projection into a skeletal structure requires a 90° rotation to either the right or the left. Alternatively, the stereochemistry can be determined and matched with the correct skeletal structure.)
Which of the following skeletal structures corresponds to the Newman projection shown?
B (m-CPBA is an acronym for meta-chloroperoxybenzoic acid. A peroxyacid is essentially a carboxylic acid bonded to a second OH group (scratch A and C). Meta means middle, as in there is a carbon that separates the two substituents bonded to the ring (scratch D).)
Which of the following structures corresponds to m-CPBA?
D (A 2° halide is one that is bonded to a 2° carbon (see questions 15 and 16). A 2° ammonium functional group is one where nitrogen has four bonds (ammonium), two of which are to carbon (2°).)
Which of the following structures has a 2º halide and a 2º ammonium functional group?
B (The reaction shown is an addition reaction, and Br2 adds to alkenes with organic solvents to form a vicinal dihalide. A three-membered bromonium ring is formed in the first step, where bromine has a positive formal charge (eliminating C and D). In order to get the stereochemistry shown in the product, this ring will form above the alkene. The second bromine attacks the more hindered carbon from underneath (an anti-addition))
Which one of the following intermediates is formed in the following reaction?
A. III < I < II (Boiling points depend on the intermolecular forces present in a molecule. These forces can be enhanced with increasing surface area (branching). Of the three isomers, II is the only one capable of hydrogen bonding, and I is less branched than III since the nitrogen has two bonding regions compared to three in III.)
Which sequence ranks the following isomers in order of increasing boiling points? A. III < I < II B. III < II < I C. II < I < III D. I < II < III
C (The conditions of the reaction promote an SN2 pathway (strong base, aprotic solvent), where one of the two methoxy groups replaces a leaving group (scratch B). The reactivity order in an SN2 reaction is 1° > 2° >> 3° (scratch A). An SN2 reaction causes an inversion of stereochemistry, but only if the reaction occurs at a chiral carbon (scratch D).)
Which starting material would form the major product shown in the highest yield?