94年國立中興大學化學所有機化學

Which is a meso compound?

(2R, 3R)-2,3-Dibromopentane

(2R, 3S)-2,3-Dibromopentane

(2R, 4R)-2,4-Dibromopentane

(2R, 4S)-2,4-Dibromopentane

Reaction of sodium ethoxide, NaOCH₂CH₃, with 1-bromopentane at 50°C yieldprimarily:

CH₃CH₂CH₂CH=CH₂

CH₃CH₂CH=CHCH₃

CH₃CH₂CH₂CH₂OH

H₃CH₂CH₂CH₂CH₂OCH₂CH₃

Which is the weakest nucleophile in polar aprotic solvents?

I⁻

Br⁻

Cl⁻

F⁻

Which of the following is not a good leaving group?

I⁻

Br^₋

CH₃O⁻

CF₃SO₃^-

One mole of each of the following alkenes is subjected to complete combustion.Which would you expect to liberate the most heat?

1-Pentane

cis-2-Pentane

2-Methyl-1-butene

2-Methyl-2-butene

How many ¹H NMR signals would trans-1,2-dichlorocyclopropane give?

1

2

3

4

Which of the following compounds give 3 signals in the broadbandproton-decoupled ¹³C NMR spectrum?

Heptane

2-Methylhexane

3,3-Dimethylpentane

2,4-Dimethylpentane

A compound with the molecular formula C₈H₉BrO gave the following ¹H NMRspectrum: δ/ppm 1.4(triplet, 3H), 3.9(quartet, 2H), 7.0(multiplet,4H). Apossible structure for the compound is:

C₆H₅OCH₂CH₂Br

p-CH₃C₆H₄OCH₂Br

p-BrC₆H₄OCH₂CH₃

p-CH_3OOC₆H₄OCH₂Br

A compound with the molecular formula C4H9Br gave the following 1H NMRspectrum: δ/ppm 1.0(triplet, 3H), 1.7(doublet, 3H), 1.8(multiplet, 2H),4.1(multiplet,1H). A possible structure for the compound is:

CH₃CH₂CHBrCH₃

CH₃CH₂CH₂CH₂Br

(CH₃)₂CHCH₂Br

(CH₃)₃CBr

Predict the base peak of mass spectrum for (CH₃)₃CCl:

m/z 15

m/z 43

m/z 57

m/z 77

The IR spectrum of a compound exhibits a broad absorption band at 2500-3000cm−1 and a sharp band at 1710 cm^−1. Which of these compounds could it be?

1-Butanol

Propyl acetate

Butanoic acid

Acetic anhydride

How many different monochlorobutanes (including stereoisomers) are formedin the free radical chlorination of butane?

1

2

3

4

Which of these compounds would exist in an enol form to the greatest extent?

Ethyl acetate

2,4-Pentanedione

Acetone

Ethanal

Which of the following compounds has the shortest carbon-carbon singlebond?

Which of the following dienes is the most reactive in the Diels-Alder reaction?

1,3-Butadiene

1,4-Pentadiene

Cyclopentadiene

1,2-butadiene

Intramolecular dehydration to form a cyclic monoester is most likely to occurwhen which of the following is heated with acid?

Which compound would have the lowest boiling point?

Rank the compounds fluorobenzene, toluene, and (fluoromethyl)benzeneaccording to their reactivity toward electrophilic aromatic substitution:

Although you might expect 1-hexyne to be more reactive in electrophilicaddition reaction than 1-hexene, the reverse is true. Explain this using yourknowledge of the mechanism of electrophilic addition to both alkenes andalkynes:

Explain why the alkane formed by hydrogenation of (S)-4-methyl-1-hexene isoptically active while the one formed by hydrogenation of (S)-3-methyl-1-pentene is not:

Explain why when propylbenzene reacts with t-butylhypochlorite threemonochlorinated products are formed in the ratios indicated: ArCHClCH₂CH₃,rCH₂CHClCH₃, and ArCH₂CH₂CH₂Cl:

Explain why the conversion of tert-butyl chloride to tert-butyl alcohol proceedfaster in 70% H₂O/30%CH₃OH than in 50%H₂O/50%acetone:

If thiophene is an aromatic molecule and reacts similarly to benzene, howmany (neutral) monobromothiophenes could be obtained in the followingreaction?

Considering both configuration and conformational factors, select the moststable form of 2,4-hexadiene:

When the 1s orbitals of two hydrogen atoms combine to form a hydrogenmolecule, how many molecular orbital(s) is (are) formed:

If all the protons of 1-fluoropentane could be discerned, which would youexpect to be at the lowest field in the ¹H NMR spectrum of this compound:

Write the structures of the three products involved in this reaction sequence:

When the following compound is treated with a strong Bronsted acid, a stablecarbocation D is formed.

(1) Propose a structure for the carbocation D, and draw its resonance structures.

(2) The proton NMR spectrum of carbocation D at –10°C consists of foursinglets at δ1.54, δ2.36, δ2.63, and δ2.82 (relative integral 2:2:2:1). Explainwhy the structure of D is consistent with this spectrum by assigning eachresonance.

(3) Explain why the NMR spectrum of D becomes a single broad line when thetemperature is raised to 113°C

Write the structure of the major organic product (E-I) for each of the followingreactions.