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Which carbanion is more stable? $$\underset{(\textbf{a})}{\ce{H2\overset{-}{C}-CN}} \qquad \underset{(\textbf{b})}{\ce{H_2\overset{-}{C}-CHO}}$$

If we talk about the −M effect, $\ce{CN}$ is higher than the $\ce{CHO}$ group in the −M group order. With this logic carbanion (a) should be more stable.

But at the same time, oxygen atom is more electronegative than the nitrogen atom. Based on this the carbanion (b) should be more stable.

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    $\begingroup$ Go with the second paragraph $\endgroup$
    – user55119
    Commented 2 days ago
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    $\begingroup$ Compare the pKa values ~25 for acetonitrile, ~13.5 for acetaldehyde $\endgroup$
    – Waylander
    Commented 2 days ago
  • $\begingroup$ a is more stable than b because -I effect of CN is more than CHO group. Either consider mesomeric effect or consider inductive effect answer will be same from both ways. $\endgroup$ Commented yesterday

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