OAT Organic Chemistry 3

Question 1

What type of isomers are (2R,3S)-2,3-dibromobutane and (2S,3R)-2,3-dibromobutane?

Accepted Answer

Enantiomers

Answer

They are non-superimposable mirror images with opposite configurations at every chiral center, making them enantiomers.

Question 2

Which reaction mechanism describes the addition of HBr to propene in the absence of peroxides?

Accepted Answer

Electrophilic addition (Markovnikov)

Answer

Without peroxides, HBr adds via electrophilic addition following Markovnikov's rule, placing Br on the more substituted carbon.

Question 3

An amide bond is best described as having which character due to resonance?

Accepted Answer

Partial double bond character (restricted rotation)

Answer

Lone pair donation from nitrogen into the carbonyl gives the C–N bond partial double bond character, restricting rotation.

Question 4

What is the major product of the dehydration of 2-methyl-2-butanol with H2SO4?

Accepted Answer

2-methyl-2-butene

Answer

Zaitsev's rule predicts preferential formation of 2-methyl-2-butene, the more substituted (more stable) alkene.

Question 5

Which spectroscopic technique is most useful for identifying the connectivity of carbon atoms in an organic molecule?

Accepted Answer

13C NMR spectroscopy

Answer

13C NMR reveals the chemical environment of each distinct carbon, mapping carbon skeleton connectivity.

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