Organic Chem 1 Lecture: Exam 2 questions from practice exam

How many elements of unsaturation do molecules with a molecular formula of C8H4N2 have?

8

Which of the following is a tertiary halide?

(CH3)2CClCH2CH3

Using Zaitsev's rule, choose the most stable alkene among the following.

(E)-hex-2-ene

Does the alkene shown below violate Bredt's rule?

no

(-)-Lactic acid has a specific rotation of -3.8°. What is the specific rotation of a solution containing 7.5 g of (-)-lactic acid and 2.5 g of (+)-lactic acid?

-1.9°

How many asymmetric carbon atoms are present in the following compound?

0

Given that glucose has a specific rotation of +52.8°. Predict the concentration of a glucose aqueous solution contained in a 10 cm long polarimetry tube if a rotation of +15.8° was observed.

0.299 g/mL

How many asymmetric carbons are present in the compound below?3-ethyl-2,2,4-trimethylpentane

1

2-methylbut-1-ene or 2-methylbut-2-ene?

2-methylbut-2-ene is more stable by 6.6 kJ/molkJ/mol.

How many elements of unsaturation are implied by the molecular formula C6H12?

1

1-bromopropane or cyclopropane

1-Bromopropane has a polar C−BrC−Br bond and has a large dipole moment. Cyclopropane has no electronegative atom and has essentially zero dipole moment.

Which of the following alkyl chlorides will undergo SN2 reaction most readily?

1-chloro-4-methylpentane

Which of the following alkyl halides reacts most rapidly via an SN1 solvolysis reaction in hot methanol?

1-iodo-1-methylcyclohexane

Which of the following alkyl halides reacts most rapidly via an SN2 reaction with NaCN?

1-iodohexane

If a mixture contains 75% of one compound and 25% of its enantiomer, what is the e.e. of the mixture?

50

Show how you would prepare cyclopentene from cyclopentane (not by dehydrogenation).

1. Br2Br2, hνhνh nu, 2. KOC(CH3)3

How many distinct alkene products results when 1-bromo-1-ethylcyclopentane is treated with NaOCH3?

2

Rank the following molecules in order of increasing relative rate of SN1 solvolysis with methanol and heat (slowest to fastest reacting).

2 < 3 < 4 < 1 < 5

Consider molecules with the formula C10H16. Which of the following structural features are not possible within this set of molecules?

2 triple bonds

Which of these double-bond isomers is more stable?

2,3-dimethylbut-2-ene

Calculate the e.e. of a mixture containing 8.0 g of (-)-glyceraldehyde and 2.0 g of (+)-glyceraldehyde.

60%

Which of the following alkyl halides is most likely to undergo rearrangement in an SN1 reaction?

2-chloro-3,3-dimethylpentane

2-methylbut-1-ene or 3-methylbut-1-ene?

2-methylbut-1-ene is more stable by 8.1 kJ/molkJ/mol.

cis-4-methylpent-2-ene or 2-methylpent-2-ene?

2-methylpent-2-ene is more stable by 6.1 kJ/molkJ/mol.

Which of the following is a geminal dihalide?

3,3-dichloropentane

Which of the alkyl chlorides listed below undergoes dehydrohalogenation in the presence of a strong base to give pent-2-ene as the only alkene product?

3-chloropentane

Which of the compounds below undergoes solvolysis in aqueous ethanol most rapidly?

3-iodo-3-methylpentane

How many elements of unsaturation are implied by the molecular formula C8H11N?

4

Use the data in Table 7-2 to predict the energy difference between 2,3-dimethylbut-1-ene and 2,3-dimethylbut-2-ene.

5.9 kJ/mol

Which of the following species is the least nucleophilic?

BF3

Which of the following compounds is the most nucleophilic?

CH3SH

Dehydrohalogenation of an alkyl halide by treating it with a strong base to yield an alkene product typically occurs by what reaction mechanism?

E2

Show how you would prepare cyclopentene from cyclopentanol.

H2SO4H2SO4, Δ

Which of the following statements correctly describe(s) E1 reactions of alkyl halides (RX)?I. Rate = k[base]II. Rate = k[base][RX]III. Rate = k[RX]IV. The reactions occur in two or more distinct steps.V. Rearrangements are sometimes seen.

III, IV, and V

ethyl chloride or ethyl iodide

Iodide has the lowest dipole moment of all four halides. Even though the C−IC−I bond length is longer than C−ClC−Cl, the larger electronegativity of ClCl makes a more significant contribution to the dipole moment. Ethyl chloride has a larger dipole moment.

Show how you would prepare cyclopentene from cyclopentyl bromide.

KOC(CH3)3

What happens to the reaction rate if the concentration of ethyl bromide is doubled?

Reaction rate doubles.

What happens to the rate if the concentration of potassium terttert-butoxide is tripled and the concentration of ethyl bromide is doubled?

Reaction rate increases six times.

Which of the following statements applies to the E2 mechanism?

The C-H and C-X bonds that break must be anti.

cis-2-3-dibromobut-2-ene or trans-2,3-dibromobut-2-ene

The isomer with two bromine atoms cis to each other will have a large dipole moment. The trans isomer has the individual bond dipole moments pointing in opposite directions, so trans-2,3-dibromobut-2-ene has essentially zero dipole moment.

Which of the statements below correctly describes an achiral molecule?

The molecule might be a meso form.

cis-1,2-dichlorocyclobutane or trans-1,3-dichlorocyclobutane

Two chlorine atoms cis to each other on a ring like cis-1,2-dichlorocyclobutane will have a large molecular dipole moment. When two chlorine atoms point in opposite directions in a molecule as in trans- 1,3-dichlorocyclobutane, they effectively cancel and the molecular dipole moment is essentially zero.

What do you expect to happen when water is shaken with ethanol (CH3CH2OH)(CH3CH2OH)?

Water and ethanol are miscible, so only one phase would appear after shaking these two together.

When trans-1-iodo-4-methylcyclohexane is heated in methanol, the product mixture is primarily ________.

a mixture of diasteromeric ethers

Which of the following best describes DDT?

a polychlorinated organic compound used as an insecticide

Is the molecule shown below chiral or achiral? (CH3)3CCH(CH3)2

achiral

Which of the following statements is (are) true for the compound (R)-2-butanol?

all of the above

Which of the following is a vicinal dihalide?

cis-1,2-dibromocyclopentane

Which of the following solvents could be described as polar and protic?

ethanol

Circle the most stable alkene in the set of isomers below.

fourth

Which of the following factors is favorable for nucleophilicity but not basicity?

highly polarizable

Which of the following is a secondary alkyl halide?

isopropyl chloride

Carbon-carbon single bonds tend to be ________ and ________ than carbon-carbon double bonds.

longer, weaker

Can the molecule shown below be properly described as a meso compound?(CH3)2CHCH2CH3

no

Water is immiscible with many _______ compounds; whether water is the top layer or bottom layer depends on whether the other material is less dense or more dense than _______.

organic and water

Show why Teflon is much more resistant to oxidation than polyethylene is.

oxidation, diradical, strong, and high

Draw the major organic product formed when the structure shown below is heated with H2SO4

pentagon with a line on the bottom

What happens to the rate if the temperature is raised?

reaction rate increases

The carbon-carbon bond length in ethylene is ________ than the carbon-carbon bond length in ethane, and the HCH bond angle in ethylene is ________ the HCH bond angle in ethane

shorter; larger than

Which of the following statements best describes the relative bond dissociation energies of the sigma and pi bonds present in the carbon-carbon double bond of an alkene?

sigma > pi

Among the following alkyl halides, choose the one with the lowest boiling point.

t-butyl chloride

Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

the same compound

cis,cis-hexa-2,4-diene or trans,trans-hexa-2,4-diene?

trans,trans-hexa-2,4-diene is more stable by 7.8 kJ/molkJ/mol.