Question

(a) How many stereoisomers are possible for 4-methyl-1,2-cyclohexanediol? ___ (b) Name the stereoisomers formed by oxidation of (S)-4-methylcyclohexene with osmium tetroxide. If there is only one stereoisomer formed, leave the second space blank. Isomer #1: Isomer #2: (c) Is the product formed in step (b) optically active? _____

Answer 1

The compound 4-methyl-1,2-cyclohexanediol has four possible stereoisomers. Oxidation of (S)-4-methylcyclohexene with osmium tetroxide yields a single product: (2S,3S)-4-methyl-1,2-cyclohexanediol, which is not optically active since it's a meso compound.

Step-by-step explanation:

The student's questions pertain to the determination of stereoisomers for a given compound, the naming of oxidation products, and the assessment of optical activity.

Part A

Regarding 4-methyl-1,2-cyclohexanediol, it has two stereocenters, leading to a maximum possible number of four stereoisomers (2n, where n is the number of stereocenters).

Part B

The oxidation of (S)-4-methylcyclohexene with osmium tetroxide leads to the formation of a single diol product, due to the syn-addition mechanism of the reaction. Therefore, only one stereoisomer is formed: (2S,3S)-4-methyl-1,2-cyclohexanediol. The second space should be left blank.

Part C

The product formed in part (b) is not optically active as it is a meso compound, meaning it has an internal plane of symmetry which compensates for its chiral centers.

Answer 2

See explanation

Step-by-step explanation:

For the first part of the question, we have to check the chiral carbons in 4-methyl-1,2-cyclohexanediol. In this case carbons, 1 and 2 are chiral, if we have 2 chiral carbons we will have 4 isomers. We have to remember that formula 2^n in which "n" is the number of chiral carbons, so:

2^n = 2^2 = 4 isomers

And the isomers that we can have are:

1) (1R,2S)-4-methylcyclohexane-1,2-diol

2) (1S,2S)-4-methylcyclohexane-1,2-diol

3) (1S,2S)-4-methylcyclohexane-1,2-diol

4) (1S,2R)-4-methylcyclohexane-1,2-diol

See figure 1

For the second part of the question, we have to remember that the oxidation with
`OsO_4` is a syn addition. In other words, the "OHs" are added in the same plane. In this case, we have the methyl group with a wedge bond, so the "OH" groups will have a dashed bond due to the steric hindrance. Due to this we only can have 1 isomer ((1S,2R,4S)-4-methylcyclohexane-1,2-diol). Finally, on this molecule, we dont have any symmetry planes (this characteristic will cancel out the optical activity), so the product of this reaction has optical activity.

See figure 2

I hope it helps!