Question

Which of the following is an acceptable structure for 2,5,5-trimethylhept-3-yne (CH3CH2)CH(CH3)C≡CCH2CH(CH3)2 CH3CH2C(CH3)2C≡CC(CH3)3 (CH3CH2)2C(CH3)C≡CCH2CH3 (CH3CH2)C(CH3)2C≡CCH(CH3)2 (CH3CH2CH2)CH(CH3)C≡CC(CH3)3

Answer 1

Answer:

D. CH₃CH₂C(CH₃)₂C≡CCH(CH₃)₂  

Explanation:

You start numbering from the end closest to the triple bond (on the right). The triple bond is between C3 and C4, and there is one methyl group on C3 and two on C5.

A. CH₃CH₂CH(CH₃)C≡CCH₂CH(CH₃)₂ is wrong. The longest chain has eight C atoms, so the compound is an octyne.

B. CH₃CH₂CH(CH₃)C≡CC(CH₃)₃ is wrong. This is a molecule of 2,2,5-trimethylhept-3-yne.

C. (CH₃CH₂)₂C≡CCH₂CH₃ is wrong. This is a molecule of 6-ethyl-5-methylhept-3-yne.

E. CH₃CH₂CH₂CH(CH₃)C≡CC(CH₃)₃ is wrong. The longest chain has eight C atoms, so the compound is an octyne.