Which of the following compounds shall not produce propene by reaction with HBr followed by elimination or direct only elimination reaction ?
- [figure]
- H3C- H2 |C-CH2OH
- H2C=C=O
- H3C- H2 |C-CH2Br
Answer
(3) H2C=C=O
Solution
(1) Cyclopropane + HBr ⇒ ring opening ⇒ CH3CH2CH2Br alc. KOH CH3CH=CH2
(2) CH3CH2CH2OH conc. H2SO4, CH3CH=CH2 + H2O (direct elimination)
(4) CH3CH2CH2Br alc. KOH CH3CH=CH2 + HBr (direct elimination)
(3) H2C=C=O (ketene) has only two carbon atoms ⇒ cannot give propene (C3H6).
Answer: (3)