IIT JEE , AIEEE Forum - Chemistry , Physical Chemistry

savvej

what is + r effect

savvej

come on someone answer???yaaar????plzzzzzzzzz

cute_ria

movement of lone pairs away from -OH group is +r effect.

mona840

+ R effect means positive resonance effect

Also known as positive mezomereic effect ( +M)

( +M grps r donating grps)

In this effect the transfer of electrons is away from an atom or substituent group

attached to the conjugate system

Example :-

Luk below at de resonating structure of aniline

Since -NH ₂increases electron density over ortho n para positions of benzene

So electrophile can attack at ortho n para positions

Tat is y + M groups are also known as ortho-para directing and activating grp

Other common xamples of +M grps r -OH & -OCH₃

savvej

plz someone tell me how does it affect bond leght as in C₂H₂Br₂

rhd92781

m not sure dis will happen or not but i dunt find any other way by which the C-H bond lenght can be affected:

Some double bond character may come in the C-H bond due to the +M effect which will shorten the bond.

rhd92781

however the second strcture may not be much stable

savvej

i was told that bond lenght in C2H2Br2 is greater(c-h bond) because of +r effect as compared to(c2h2,c2h4 and c6h6).
someone plzzzzzzzz help.

kane

rhd told you that the second structure might not be stable and he's right.since the structure is not stable due to positive charge acquired by carbon its bond order will be less and hence bond length will be greater

savvej

but still i m not getting how can we say that bondl eght will increase .plzz help(i have given thumbs up to all for your efforts).but still my doubt is not clarified.

kane

jo diagram rhd ne draw ki hain uske baad he posted that the second structure might not be stable and he's right the second structure is not stable because carbon gets positive charge acquired on itself which makes the compound unstable due to which bond order decreases and hence bond length increases

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