Posted by: Mark Foreman | February 21, 2012

Alternative to nitrobenzene

Dear Reader,

I am sure that many of you will be aware that nitrobenzene is an important industrial chemical, it is needed for the production of aniline. In November 2005 a serious accident occurred in China which caused about 100 tons of nitrobenzene (and related chemicals) to enter the Songhua River. This pollution event did cause the bacterial life in the river to change.

When I was discussing the chemistry of nitrobenzene today, one of the students asked why it can not form a three membered (NO2) ring to form 3-phenyl-1,2,3-dioxaziridine rather than nitrobenzene.

I think that the reason is ring strain. Crude molecular mechanics predict that 3-phenyl-1,2,3-dioxaziridine has an energy of 131.6316 kcal/mol while nitrobenzene has an energy of only 117.5358 kcal/mol.

Molecular mechanics gets the structure of nitrobenzene wrong, while steric effects might try to move the nitro group so the O-N-O atoms are in a different plane to the carbon atoms of the ring, electronic effects will make the nitro group coplannar with the benzene ring.

I have attached the atomic coordinates of the two molecules to the bottom of this post. I hope to add pictures soon.

C(1) -3.7091 1.4828 -0.0013
C(2) -3.2163 0.2890 0.3645
C(3) -3.9900 -0.8109 0.3191
C(4) -5.2643 -0.6995 -0.0980
C(5) -5.7583 0.4937 -0.4643
C(6) -4.9809 1.5864 -0.4162
N(7) -3.5226 -1.9411 0.6661
O(8) -3.6007 -2.2668 1.7501
O(9) -3.0350 -2.6051 -0.1140
H(10) -3.0685 2.3798 0.0390
H(11) -2.1685 0.2191 0.7037
H(12) -5.9154 -1.5894 -0.1426
H(13) -6.8040 0.5767 -0.8051
H(14) -5.3863 2.5670 -0.7168

 

C(1) -5.5159 -1.1850 1.0942
C(2) -4.8200 -0.0531 1.2832
C(3) -4.6720 0.8757 0.3141
C(4) -5.2670 0.6060 -0.8721
C(5) -5.9658 -0.5235 -1.0723
C(6) -6.0944 -1.4258 -0.0900
N(7) -3.9492 1.8904 0.7478
O(8) -4.5189 2.8940 0.0608
O(9) -3.3218 2.2337 -0.3891
H(10) -5.6135 -1.9191 1.9118
H(11) -4.3618 0.0991 2.2775
H(12) -5.2127 1.2926 -1.7351
H(13) -6.4393 -0.7146 -2.0505
H(14) -6.6680 -2.3531 -0.2535
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