A) \[:C{{H}_{2}}CHO\]
B) \[\overset{+}{\mathop{C}}\,{{H}_{2}}CHO\]
C) \[\overset{+}{\mathop{C}}\,{{H}_{2}}OH\]
D) \[:\bar{C}HCHO\]
Correct Answer: A
Solution :
The \[\alpha \]-hydrogen atoms of acetaldehyde due to \[-E\]effect of\[\rangle C=O\]group is slightly acidic in nature. In crossed aldol condensation between formaldehyde and acetaldehyde, in the first step\[O{{H}^{-}}\]ion (from the base added) abstracts one of these acidic a-hydrogen to form carbaplion or enolate ion which is stabilized by resonance. \[H{{O}^{-}}+H-C{{H}_{2}}-\overset{\begin{smallmatrix} O \\ || \end{smallmatrix}}{\mathop{C}}\,-H\overset{Slow}{\mathop{\rightleftharpoons }}\,\] \[{{H}_{2}}O+_{\bullet }^{\bullet }C{{H}_{2}}-\overset{\begin{smallmatrix} O \\ || \end{smallmatrix}}{\mathop{C}}\,-H\]
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