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how to write mesomeric effect of +m&-m
The mesomeric effect or resonance effect in chemistry is a property of substituents or functional groups in a chemical compound. The effect is used in a qualitative way and describes the electron withdrawing or releasing properties of substituents based on relevant resonance structures and is symbolized by the letter M. The mesomeric effect is negative (-M) when the substituent is an electron-withdrawing group and the effect is positive (+M) when based on resonance and the substituent is an electron releasing group.

    Examples of -M substituents: acetyl (IUPAC ethanoyl) - nitrile - nitro
    Examples of +M substituents: alcohol - amine-benz


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