Di-derivatives x x x p v as $ v as s Here we have assumed the substituent groups to be alike; when they are unlike, a greater number of isomers is possible.
Orientation of Substituent Groups.-The determination of the relative positions of the substituents in a benzene derivative constitutes an important factor in the general investigation of such compounds.
Intermolecular transformations-migrations of substituent groups from one carbon atom to anotherare of fairly common occurrence among oxy compounds at elevated temperatures.
Not only does the substituent group modify the readiness with which the derivative is attacked, but also the nature of the product.
Starting with a monoderivative, we have seen that a substituent group may enter in either of three positions to form an ortho-, meta-, or paracompound.
Soc. 61, p. 367): If the hydrogen compound of the substituent already in the benzene nucleus can be directly oxidized to the' corresponding hydroxyl compound, then meta-derivatives predominate on further substitution, if not, then orthoand paraderivatives.
3 1 tri-derivatives, except in such cases as when both substituent groups are strongly acid, e.g.
Bamberger (a strong supporter of the centric formula), have shown that the nature of the substituent groups influences the distribution of the fourth valencies; therefore it may be con-?
The mere retention of the same crystal form by homologous substances is not a sufficient reason for denying a morphotropic effect to the substituent group; for, in the case of certain substances crystallizing in the cubic system, although the crystal form remains unaltered, yet the structures vary.
Other substituent groups exercise morphotropic effects similar to those exhibited by the alkyl radicles; investigations have been made on halogen-, hydroxy-, and nitro-derivatives of benzene and substituted benzenes.
formula also allows of the existence of six di-derivatives, six tri-derivatives, three tetraand one penta derivative, when the substituent groups are identi N %"cal; all of which are in agreement with known facts.
The nature of the substituent exerts a specific influence on the reaction; thus with chlorine or bromine, ortho-semidines and the diphenyl bases are the chief products; the dimethylamino, -N(CH 3) 2, and acetamino, -NHCOCH3, groups give the diphenyl base and the para-semidine respectively.
The cyano substituent also reduces the barrier height 3-2 ' from 5.3 to 0.3 kcal mol -1.
Bonds marked with b carry a benzo substituent, omitted here for clarity.
substituent in the adjacent meta position should avoid this clash and permit an additional interaction with the enzyme (J.H.
substituent electronic effects.
substituent groups are different, then the molecule will be chiral.
Aromatic fluorine substituent improves bioavailability and increases potency, but it is not critical.
from acetylene and acetone); but according to Baeyer (Ber., 1886, 9, 1797) it fails to explain the formation of dioxyterephthalic ester from succinosuccinic ester, unless we make the assumption that the transformation of these substances is attended by a migration of the substituent groups.
The magnitude of this separation would obviously depend on the magnitude of the substituent group, which may be so large (in this case propyl is sufficient) as to cause unequal horizontal deformation and at the same time a change in the vertical direction.
If, however, one of the para positions in the hydrazo compound is substituted, then either diphenyl derivatives or azo compounds are formed, or what is known as the semidine change takes place (P. Jacobson, Berichte, 1892, 2 5, p. 99 2; 1893, 26, p. 681; 1896, 29, p. 2680; Annalen, 1895, 287, p. 97; 1898, 3 0 3, p. 290) A para mono substituted hydrazo compound in the presence of a hydrochloric acid solution of stannous chloride gives either a para diphenyl derivative (the substituent group being eliminated), an ortho-semidine, a para-semidine, or a diphenyl base, whilst a decomposition with the formation of amines may also take place.
A suitable substituent in the adjacent meta position should avoid this clash and permit an additional interaction with the enzyme (J.H.
Kinetic and thermodynamic stabilization will be provided via extensive spin delocalization and substituent electronic effects.
If the substituent groups are different, then the molecule will be chiral.
The measure of the loss of symmetry associated with the introduction of alkyl groups depends upon the relative magnitudes of the substituent group and the rest of the molecule; and the larger the molecule, the less would be the morphotropic effect of any particular substituent.
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