Which compound does not react with nucleophiles?
CH3COCH3\text{CH}_3\text{COCH}_3CH3COCH3
CH3CH2CHCH2\text{CH}_3\text{CH}_2\text{CHCH}_2CH3CH2CHCH2
CH3CHO\text{CH}_3\text{CHO}CH3CHO
CH3CH2Br\text{CH}_3\text{CH}_2\text{Br}CH3CH2Br