Question

7. An unknown compound, C8H14, is optically active. Hydrogenation of the unknown
yields 4-methylheptane. Ozonolysis of the unknown yields ethanol and 2-
methylpropandial. Suggest a structure for the unknown consistent with the above date.

please help

Answer 1

With all this type of problem start by calculating the number of double bond equivalents.

see (Broken Link Removed)

So here the DBE = {(2x8+2)-(14-0)}/2

=4/2=2

The hydrogenation product tells the carbon structure

CH3-CH2-CH2-CH(CH3)-CH2-CH2-CH3

and so the unknown contains two double bonds or one triple bond

If ozonolysis gives us

O=CH-CH(CH3)-CH=O

plus ethanal

then the structure is

CH3-CH=CH-CH(CH3)-CH=CH-CH3

Which is two DBE.

The structure is only chiral if one double bond is Z and the other E.

So there are four possible structures:

(R)-2Z,5E-4-methylhepta-2,5-diene
(R)-2E,5Z-4-methylhepta-2,5-diene
(S)-2Z,5E-4-methylhepta-2,5-diene
(S)-2E,5Z-4-methylhepta-2,5-diene

Answer 2

I think I have the absolute configurations correct, but please check using a model.