Experimentally it has been determined that -OH shows less negative inductive effect than -OR (R being an alkyl group) but this is counterintuitive considering that -R is an electron donating group which increases the electron density on O reducing its electron withdrawing capacity. Is there any intuitive reasoning behind this order? Can a similar reason be used to explain why NHR (R being an alkyl group) shows more inductive effect than -NH2 or is there a different reason for this?
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1$\begingroup$ Its strange but the bond angle in -OCH3 being more than in -OH also means more s character for the O in -OCH3 and hence more -I.The same reason goes for -NHR. $\endgroup$– NightwingCommented Nov 13 at 20:38
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$\begingroup$ How do we assume that more bond angle means more s character. Isn't the reverse only true? $\endgroup$– MayoCommented Nov 15 at 9:41
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1$\begingroup$ Its related to the bent rule where a higher bond angle means more s character for the orbitals. $\endgroup$– NightwingCommented Nov 16 at 16:07
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$\begingroup$ In fact, R is NOT an inductive electron-donating group. pubs.rsc.org/en/content/articlelanding/2024/ob/d4ob01572j A small number of people have been saying this for over 50 years, and yet the myth remains. $\endgroup$– mcelliott29googlemailcomCommented Dec 3 at 7:54
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$\begingroup$ Ah yes, I was wondering when this will make it's presence here. This is an interesting work, but I'm afraid, this is much more a comment than an actual answer. This does deserve more explanation. And I really want to upvote it... $\endgroup$– Martin - マーチン ♦Commented Dec 3 at 17:07
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1 Answer
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The answer to your first question could be that in -OMe, methyl being a larger group than Hydrogen, would face more repulsion from the non bonding electron pairs of oxygen, this would effectively increase its bond angle... We also know that as bond angle increases, electronegativity increases. (Recall sp hybridisation has a bond angle of 180 degree and it is the most electronegative, whereas sp2 having a bond angle of 120 degree, is comparitively less electronegative.) Hence -OMe's group electronegativity would be higher than that of -OH
