Question

A common compound A is prepared from phenol and oxidized to compound B. Dehydration of A with H₂SO₄ leads to compound C and treatment of A with PBr₃ gives D.In the mass spectrum of D there is a very strong peak at m/e = 83 (base peak) and two molecular ion peaks at m/e 162 and 164.The ratio of intensities of the peaks 162 and 164 is 1.02. Compound D can be converted to an organomagnesium compound E that reacts with a carbonyl compound F in dry ether to give G after hydrolysis. G is a secondary alcohol with the molecular formula C₈H₁₆O. 

(a) Outline all steps in the synthesis of G and draw the structural formulae of the compounds A – G. 

(b) Which of the products A – G consist of configurational stereoisomeric pairs?

(c) Identify the three ions in the mass spectrum considering isotopic abundances given in the text.

Answer 1

(b) G has two stereoisomeric pairs since it has a chiral carbon. 

(c) The base peak at m/e = 83 is due to the cyclohexyl-cation,C₆H₁₁, the peaks at m/e = 162 and 164 show the same ratio as the abundance of the two bromine isotopes. Therefore, they are the molecular peaks of bromocyclohexane.