Chemistry - Halogen Derivative Question with Solution | TestHub
How many of the following alkanes can be prepared by the Wurtz reaction (Na/dry ether) from a single monohaloalkane (R-X), i.e. as R-R?
Answer:
Solution:
A single monohaloalkane R-X with Na/dry ether gives R-R (Wurtz reaction): 2R-X + 2Na → R-R + 2NaX. So the alkane must split into two identical alkyl groups at one C-C bond, which needs an even number of carbons and a symmetric structure.
(i) butane (C₄) = ethyl + ethyl: yes.
(ii) hexane (C₆) = propyl + propyl: yes.
(iii) 2,4-dimethylpentane (C₇): odd carbons, no.
(iv) 2,5-dimethylhexane (C₈) = isobutyl + isobutyl: yes.
(v), (vi) cyclooctane and cyclopentane need a dihaloalkane, not a single monohaloalkane: no.
(vii) propane (C₃) and (ix) pentane (C₅): odd carbons, no.
(viii) 2,2,4-trimethylpentane (C₈): the two halves are not identical, no.
So (i), (ii) and (iv) qualify. Answer = 3.
