9701 MCQ Solution 20

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Question 20: [Organic > Introductory Organic]:
The Russian composer Borodin was also a research chemist who discovered a reaction in which two ethanal molecules combine to form a compound commonly known as aldol (reaction I). Aldol forms another compound on heating (reaction II).

I 2CH3CHO àCH3CH(OH)CH2CHO
II CH3CH(OH)CH2CHO à CH3CH=CHCHO + H2O

Which of the following describes reactions I and II?


I
II
A
addition
elimination
B
addition
reduction
C
elimination
reduction
D
substitution
elimination

Reference: Past Exam Paper – November 2002 Paper 1 Q20



Solution 20:
Answer: A.

In the first reaction 2 molecules, regardless of the fact that it is the same molecule, combine to form 1 product, which can only be defined as an addition reaction, eliminating options C and D. 
The second reaction is a form of dehydration which in turn categorises under elimination reactions (it eliminates water molecules). 

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