Chemistry ELECTROMERIC EFFECT

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ELECTROMERIC EFFECT

Electromeric Effect :

In presence of an electrophile, there is complete transfer of `pi`-electrons from one atom to produce temporary on atoms joined by multiple bonds; it is called Erectromeric effect. See fig.

If electrophile is removed, charge disappears and substrate attains its original form. Thus this effect is reversible and temporary.

Positive Electromeric Effect :

When `pi`-electrons transfer takes place `C` to `C` (as alkenes, alkynes etc.) it is called Positive Electromeric effect (denoted by `E_+`). See fig.1.

In this there is also (`+I`) effect of `- CH_3` group which cause `pi`-electron transfer from `C_2` to `C _1`. `CH_3 -CH=CH-CH_2CH_3`

(`+I`) effect of `CH_3CH_2-` is larger than that of `CH_3-`, hence `pi` electron transfer is from `C_3` to `C_2`. See fig.2.

Negative Electromeric Effect :

When `pi`-electrons transfer takes place to more electronegative atom (`O`, `N`, `S`) joined by multiple bonds, it is called Negative Electromeric Effect (denoted by `E_-`). See fig.