Racemic mixture and plane polarized light

[jjunior]

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Hello, i was reading through BR OChem chapter 3 and came aross this example.

Example 3.17
Which of the following reactions produces no optically active compounds?
A. 2-Butanone treated with NaBH4 in ether followed by acidic workup.
B. (Z)-2-butene with KMn04 in base (syn addition of two hydroxyl groups).
C. Reduction of HN=C(CH3)CH2CH3 using LiAlH4 in the solvent.
D. S-2-Bromobutane treated with NaCN in ether solvent.

The answer is B, and im wondering could A also be correct? since A forms a racemic mixture (2 enantiomers in equal proportion)? and racemic mixture does not rotate plane polarized light and thus optically inactive? or am i not suppose to assume that the 2 products are produced in equal quantities??

 

[Jepstein30]

Hello, i was reading through BR OChem chapter 3 and came aross this example.

Example 3.17
Which of the following reactions produces no optically active compounds?
A. 2-Butanone treated with NaBH4 in ether followed by acidic workup.
B. (Z)-2-butene with KMn04 in base (syn addition of two hydroxyl groups).
C. Reduction of HN=C(CH3)CH2CH3 using LiAlH4 in the solvent.
D. S-2-Bromobutane treated with NaCN in ether solvent.

The answer is B, and im wondering could A also be correct? since A forms a racemic mixture (2 enantiomers in equal proportion)? and racemic mixture does not rotate plane polarized light and thus optically inactive? or am i not suppose to assume that the 2 products are produced in equal quantities??

The question isn't asking about the overall polarization of the mixture.. it's asking about the optical activity of each compound.

A solution containing the reaction described in A would be racemic and optically inactive.. but each compound individually is optically active. Hence it's incorrect. None of the compounds in B rotate plane-polarized light.

 

[jjunior]

that makes sense , thnx!