A2 Optical Isomerism Question.Watch
"One optically active isomer of 2-chlorobutane reacts with hydroxide ions to form butan-2-ol. The organic product is mixture of enantiomers because:
A) Butan-2-ol contains a chiral carbon atom.
B) The reaction is a nucleophilic substitution.
C) 2-chlorobutane forms a carbocation intermediate.
D) 2-chlorobutane forms a five-bonded transition state."
Now I don't get it because obviously it's a primary halogenoalkane and those undergo SN2 reactions which only give one optical isomer of the alchohol. So how come there's a mixture here and how come the answer's C?
"This is because the carbocation formed in the rate determining step (b) (i), has a trigonal planar arrangement of C-R bonds around the C+ carbon, so the hydroxide ion (or water) can attack each side of the carbocation with equal probability, giving equal amounts of each possible optical isomer. The two optically activities cancel each other out, so zero rotation of plane polarised light."
Website: http://www.docbrown.info/page07/isomerism2a.htm (case study 2b.5)