Which of the following is a valid resonance contributor of methyl vinyl ether, $CH X_{2} = CH - O - CH X_{3}$ ?

A $CH X_{3} - CH X_{2} - CH = O$
B $CH X_{3} - CH = CH - OH$
C $X_{+} X_{2}^{2 +} CH X_{2} - CH X_{2} - O - CH X_{3}$
D $X_{-} X_{2}^{2 -} CH X_{2} - CH = O X^{+} - CH X_{3}$

Answer: D

Resonance structures differ only in the positions of electrons, not of atoms. Pushing the oxygen lone pair towards carbon and the pi bond onto the terminal carbon gives

X_{-} X_{2}^{2 -} CH X_{2} - CH = O X^{+} - CH X_{3}

CH X_{3} - CH X_{2} - CH = O

and

CH X_{3} - CH = CH - OH

are constitutional isomers (atoms moved), and the last structure has a different formula.

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Which of the following is a valid resonance contributor of methyl vinyl ether, CHX2​=CH−O−CHX3​?

Answer: D

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Which of the following is a valid resonance contributor of methyl vinyl ether, $CH X_{2} = CH - O - CH X_{3}$ ?