ORGO 1 Uworld

SN1 rxn example

Prenyl bromide is classified as an allylic substrate that favors either SN1 or SN2 reactions. Since methanol is a weak nucleophile and the reaction requires heat, an SN1 reaction mechanism is favored. Bromide acts as the LG, and a primary allylic carbocation forms when bromide leaves

Proton nuclear magnetic resonance detects protons in a molecule by applying an external magnetic field and radio frequencies to a sample

Protons shielded by nearby electrons have smaller chemical shifts (upfield). Deshielded protons, such as those near electronegative atoms, have larger chemical shifts (downfield).

sugar stereoisomers (types of epimers)

Sugar stereoisomers that differ in orientation at only one stereocenter are known as epimers, a specific kind of diastereomer. If the sugars differ in configuration at only the anomeric carbon (denoted by α and β in the sugar's name), they are classified as anomers, a special kind of epimer.

Structural isomers

also called constitutional isomers, differ in how the atoms are connected at one or more points within the structure.

Epimers

are a type of diastereomer that differ in spatial orientation at only one stereocenter.

Conformational isomers

are structures that have the same formula and connectivity, and can be interconverted by the rotation of σ bonds. Because conformational isomers are identical except for structural bond rotations, they are the same compound.

acids catalyze many reactions by

donating protons to a reactant. Protonation enhances electrophiles and increases the stability of leaving groups. Acids generally decrease the nucleophilicity of molecules.

Which is the best leaving group? F, Cl, Br, or I

iodide is the best leaving group because it is the largest halide and can best stabilize the negative charge upon anion formation.

Suppose that a 0.2 g/mL solution of (S)-ibuprofen in a 2 dm long cell rotates plane-polarized light +10°. What is the specific rotation for (S)-ibuprofen?

+25 degrees

Based on the specific rotation stated in the passage, what would be the observed rotation of NNG3 if a 2.0 × 10−3 g/mL sample in a 0.50 dm cell were used to take the measurement?

-0.35 degrees

Compared to hands washed with no soap, washing hands with 3.0 mL of soap reduced bacteria recovered per hand by a factor of approximately:

100

How many degrees of unsaturation are present in a compound with molecular formula C8H13OCl?

2 degrees

When the compound shown below undergoes an SN2 reaction with hydroxide, which of the following compounds will most likely form as the major product?

2-chloro-2-(fluoromethyl)propane-1,3-diol

Compared to the enolate intermediate shown in Figure 3, the quinonoid intermediate in Figure 2 is: A.less stable because of its greater number of resonance forms. B.less stable because of its increased delocalization of electron density. C.more stable because of its expanded network of conjugated pi bonds. D.more stable because of its smaller number of resonance forms.

A conjugated system is stabilized through electron delocalization via resonance, the distribution of electrons through alternating pi bonds. Conjugated molecules can be identified by alternating single bonds and double or triple bonds.

Selecting the best electrophile for an SN2 Reaction

An SN2 reaction is a second-order substitution that takes place in a single, concerted reaction step between the electrophile and nucleophile. SN2 reactions tend to require a strong nucleophile and occur the fastest with sterically unhindered electrophiles; tertiary electrophiles are unable to participate in SN2 reactions.

Which of the following is true regarding the relative stability of carbocation and carbanion species as the number of alkyl substituents increases relative to hydride substituents? A.As the number of alkyl substituents increases, carbocation stability increases but carbanion stability decreases. B.As the number of alkyl substituents increases, carbocation stability decreases but carbanion stability increases. C.As the number of alkyl substituents increases, carbocation stability and carbanion stability both increase. D.As the number of alkyl substituents increases, carbocation stability and carbanion stability both decrease.

A.As the number of alkyl substituents increases, carbocation stability increases but carbanion stability decreases. (68%)

Suppose that NaI was replaced with another nucleophile in Experiment 1. Which of the following anions would be the most nucleophilic? A.CH3(CH2)2CH2− B.(CH3)2N− C.CH3CH2O− D.F−

A.CH3(CH2)2CH2− The charged carbon atom of CH3(CH2)2CH2− is less electronegative than the nitrogen atom of (CH3)2N−, the oxygen atom of CH3CH2O−, and the fluorine atom of F−. Therefore, electrons on a negatively charged carbon atom are less stabilized and more easily shared with an electrophile, making CH3(CH2)2CH2− the best nucleophile.

Can α-D-fructose and β-D-fructose be classified as anomers? A.Yes, because they are ketoses that differ in configuration at C2 only. B.Yes, because they differ in configuration at more than one carbon. C.Yes, because they are C1 epimers. D.No, because they are enantiomers.

A.Yes, because they are ketoses that differ in configuration at C2 only. For aldoses such as glucose, the anomeric carbon is C1, whereas for ketoses such as fructose, the anomeric carbon is C2. α-D-fructose and β-D-fructose are diastereomers that differ in orientation at C2 (the anomeric carbon) only. Therefore, α-D-fructose and β-D-fructose are anomers.

Acid helps catalyze the Fischer esterification reaction by doing all of the following EXCEPT: A.enhancing the nucleophilicity of alcohols. B.forming a resonance-stabilized intermediate. C.creating a good leaving group. D.increasing carbonyl electrophilicity.

A.enhancing the nucleophilicity of alcohols.

If a primary alkyl halide and a chiral tertiary halide both undergo substitution reactions, the reaction with the tertiary halide will have more products because: A.the primary halide undergoes an SN2 reaction, which occurs in one step and is not stereospecific. B.the chiral tertiary halide undergoes an SN1 reaction, which forms a carbocation and is not stereospecific. C.the nucleophile can add to the electrophile from either side of the primary alkyl halide. D.the backside of the electrophilic carbon on a tertiary halide is not sterically hindered.

B.the chiral tertiary halide undergoes an SN1 reaction, which forms a carbocation and is not stereospecific.

Which of the following statements do NOT correctly describe a contributing factor for the increased reactivity of cyclopropane versus cyclohexane? A.The carbon-carbon sigma bonds have poor orbital overlap. B.The bond angle in cyclopropane is compressed to 60°. C.Cyclopropane has a lower boiling point. D.The C-H bonds in cyclopropane are permanently eclipsed.

C. Cyclopropane has a lower boiling point.

Which term can be used to classify the relationship between two isomers that have the same connectivity but specific rotations of +40° and −25°, respectively? A. Enantiomers B. Racemic mixture C. Diastereomers D. Conformational isomers

C. Diastereomers

Would (R,R)- and (S,S)-labetalol be expected to rotate plane-polarized light in the same direction? A.Yes, because they are diastereomers. B.Yes, because the rotations would have the same magnitude. C.No, because they are enantiomers. D.No, because the rotations would cancel out each other.

C. No, because they are enantiomers.

Which of the following statements is NOT supported by the results in Tables 1 and 2? A.In Experiment 2, crotyl chloride forms a stable carbocation. B.Primary alkyl halides react more readily in SN2 reactions than in SN1 reactions. C.Nucleophilic substitution reactions are not dependent on the substrate (alkyl halide) substitution. D.Bromide is a better leaving group than chloride and enhances reactivity in less favorable reactions.

C.Nucleophilic substitution reactions are not dependent on the substrate (alkyl halide) substitution. Observations for the SN2 reaction conditions (Table 1) show that 1-bromobutane (a primary halide) formed a precipitate whereas tert-butyl chloride (a tertiary halide) did not react, even after heating. Conversely, results for the SN1 reaction conditions (Table 2) record that tert-butyl chloride formed a heavy precipitate, but 1-bromobutane only formed a trace amount of precipitate after heating. This data demonstrates that SN1 and SN2 reactions are dependent on substrate substitution because primary and tertiary alkyl halides react only in certain conditions.

Suppose the HPLC experiment used to generate Figure 3 is repeated, but the sample is contaminated. If the results include a new peak with a retention time of 23.421 minutes, the contaminant most likely: A.has a lower affinity for the stationary phase than vitamin K quinone. B.has a lower affinity for the stationary phase than vitamin K 2,3-epoxide. C.has a lower affinity for the mobile phase than vitamin K 2,3-epoxide. D.has a lower affinity for the mobile phase than vitamin K hydroquinone.

C.has a lower affinity for the mobile phase than vitamin K 2,3-epoxide.

The inductive effect occurs when electron density is donated through sigma bonds

Carbocations are stabilized by electron donating groups because they donate electrons to the positively charged carbon; they are destabilized by electron withdrawing groups because they pull electrons away from the carbocation, creating two adjacent positive charges

Based on Figure 2, which amino acid residue in FIX most likely undergoes carboxylation during Reaction 1? A.Aspartate B.Asparagine C.Glutamine D.Glutamate

D. Glutamate

Based on the NMR results described in the passage, what effect does the addition of calcium ions have on the protons that corresponded to the 1 ppm peak? A.Calcium ions cause additional splitting of the 1 ppm peak. B.Calcium ions reduce the splitting of the 1 ppm peak. C.Calcium ions result in shielding of the protons that corresponded to the 1 ppm peak. D.Calcium ions result in deshielding of the protons that corresponded to the 1 ppm peak.

D.Calcium ions result in deshielding of the protons that corresponded to the 1 ppm peak.

Steric hindrance is a characteristic bulkiness in compound structures that either blocks a portion of a molecule so that it cannot react or keeps a reaction from occurring altogether.

Decreasing the substitution on (or near) an atom decreases the steric hindrance of the atom.

The rate of substitution reactions can be impacted by structural features of either the nucleophile or the electrophile.

First-order (SN1) substitution reactions are zero order with respect to the nucleophile, and the identity of the nucleophile will not affect the rate of SN1 product formation.

The following plot depicts the torsional energy of 2-methylbutane as it rotates about the C2-C3 bond. Which point on the energy plot corresponds to the Newman projection shown above?

I

(S,R)- and (R,R)-labetalol, the active forms of the drug, can be described as which of the following? I. Diastereomers II. Enantiomers III. Conformational isomers

I only

Which of the following characteristics is(are) shared by constitutional isomers? I. Same molecular formula II. Nonsuperimposable mirror images III. Different connectivity of atoms IV. Usually have different physical properties

I, III, and IV only

The substrate tert-butylchloride reacts in Experiment 2 but not in Experiment 1 because: I. the leaving group of tert-butylchloride is bonded to a primary carbon. II. a stable carbocation forms in Experiment 2. III. the leaving group of tert-butylchloride is bonded to a tertiary carbon. IV. an unstable carbocation forms in Experiment 2.

II and III only

Which condensed structure(s) contain an ether functional group? I. CH3CH2CO2CH2CH3 II. CH3CH2OCH2CH3 III. CH3CH(OH)CH2CHO IV. CH3O(CH2)3CHO

II and IV only Ethers are an oxygen-containing functional group with the general formula R-O-R', where the R groups are two alkyl groups.

The rate-limiting step in an SN1 reaction is the formation of the initial carbocation.

Molecular features that impact carbocation stability have an impact on the rate of SN1 reactions. Tertiary carbocations have the greatest stability and provide the highest rate of SN1 reactions.

The extent of a substrate's steric hindrance can dictate which nucleophilic substitution (SN1 or SN2) it is likely to undergo.

SN1 reactions permit sterically hindered electrophiles whereas SN2 reactions require easily accessible electrophiles.

Polar aprotic solvents and SN2 reactions

SN2 reactions are promoted by polar aprotic solvents, which facilitate formation of the transition state without diminishing the strength of the nucleophile. Dimethylsulfoxide (DMSO) is a polar aprotic solvent.

Isomers are different compounds with the same molecular formula, and some reactions produce a mixture of isomers.

The major product of a reaction is dependent on the reaction conditions: The more stable product will predominate under thermodynamic conditions, and the less stable product will predominate under kinetic conditions. If one compound is more stable than the other then the more stable one will have a greater amount in the mixture

Tautomerization is a type of isomerization involving the transfer of a hydrogen atom from one position to another in a molecule and the movement of a double bond

The nucleotides can tautomerize, with guanine and thymine shifting between keto (major) and enol (minor) forms whereas adenine and cytosine shift between amines and imines.

Why does the bond between glycerol and the 2-ethylhexyl group tend to form at glycerol's C1 hydroxyl group instead of the C2 hydroxyl group? A.Secondary alcohols are more likely to undergo SN1 reactions than primary alcohols. B.Secondary alcohols are more sterically hindered than primary alcohols. C.Primary alcohols are less acidic than secondary alcohols. D.Primary alcohols are more electrophilic than secondary alcohols.

The passage states that ethylhexyl glycerin forms in an SN2 reaction. The alcohol on carbon 2 of glycerol is a secondary alcohol, whereas carbon 1 is a primary alcohol, and the added steric hindrance at carbon 2 prevents SN2 reactions from happening as readily as they do at carbon 1. Therefore, the C1 hydroxyl group reacts with an ethylhexyl halide more easily than the C2 hydroxyl group does.

SN2 reactions with bulky nueclophiles

The structure of a nucleophile can impact its steric hinderance and capacity to react with electrophiles. Bulky nucleophiles are less able to approach an electrophilic carbon atom during a substitution reaction and will lead to a slower rate of reaction.

The reaction catalyzed by glutamate racemase produces ᴅ-glutamate from its substrate ʟ-glutamate, which has an S absolute configuration.

Therefore, the correct answer should show glutamate with an S configuration at the α-carbon.

If 3-bromo-2,4-dimethylpentane (shown below) was used as a substrate in the experiments described in the passage, what would the observation be for reaction with NaI at 25°C?

Trace precipitate, because the methyl groups hinder the addition of iodide to the electrophile

Many of the bonds in vitamin K have angles of 120°. Which reaction in Figure 1 results in one or more new bonds with angles of less than 120°?

reaction 1 only

In the oxidation of vitamin K hydroquinone to vitamin K 2,3-epoxide, hydroxyl groups are converted to carbonyls. Compared to the carbon-oxygen bonds of the hydroxyl groups, the carbonyl carbon-oxygen bonds are characterized by:

side-to-side overlap of p orbitals

In Reaction 1, what hybridization state changes do the methylated carbon atom in the ringed structure of vitamin K hydroquinone and the oxygen atom involved in epoxide formation undergo?

sp2 to sp3 for the methylated carbon and sp2 to sp3 for the oxygen atom

Enantiomers and specific rotation

specific rotation is the normalized degree to which chiral molecules rotate plane-polarized light. Enantiomers each rotate plane-polarized light by the same magnitude in opposite directions

The number of stereoisomers possible for a given molecule is 2n. The variable n denotes the number of:

stereocenters

Decarboxylation is

the removal of a carboxyl group with the release of CO2

The experimental data obtained when a chiral molecule interacts with plane-polarized light is called:

the specific rotation

Why was the optimization for the oxidation of Compound 3 monitored by thin-layer chromatography? The resulting TLC plate given in the passage is used to determine:

which reaction conditions provide the greatest amount of Compound 4 and the least amount of Compound 5. compound 4 is the product and compound 5 is side product

Do the compounds have the same stereochemical configuration?

yes the stereocenters are both S