399%
instirute of Chernis?r)/,l!niversity of Wrociairv, Wroclaw, Poiand
(Received May 17, 7972)
An extension of Mulliken's charge-transfer theory leads to a relation between the enhancement of dipole xnomevit and the ionization potential of donors of structurally similar hydrogen-bonded complexes, Experimental data of hydrogen-bonded systems formed between 3,s-dinitrophenol and amines are in agrreInept with theoretical prediction. I t is shown that the observed polarity of the hydrogen bond in the systenis studied is connected with the electron delocalization effect.
One of the more important experimental properties of hydrogen-bonded complexes is the electric dipole moment. This quantity can give valuable information on. the bonding character of the complex. However, so far the origin of the observed enhancement of dipole moment of hydrogen-bonded cornpkxes has nat been completely elucidated; whether it i s connected with the existence of tautomeric equailibriitln between molecular and ion-pair species as a ~ o r i ~ e ~ of ~ the e ~ proton-transfer ~ c e effect,2 or wcth the electron delocaiization '( charge-transfer) effect i s still a matter of i?uch d e l ~ a t e . ~ , ~ The ]purpose ~f the preaerkt work is to give some strong support in favor of c h a r p t r a n s f e r theory of the hydrogen b0nd.~--5This nim will be pursued by the discussion, zsing Mulliken '5; ckiaip transfer theory, or' correlation found between the enhancement of dipole moment and ionization potent,ial of the donor for some hydrogen-bonded complexes formed between 3,s-dinitrophenol and several amines. 7-l 'The a r d y s i s d.eveloped here leads to the evaluation of some important structural parameters (60 = HOI- SWO; EAL'-b C) of hyd.roaerr.-eoaded complexes and throws new light or1 the nature of this type interaction. ewetical
Therefore, we can write + - - +
A/.i
APind
--B
ADCT
(4)
According to Mulliken's charge-transfer theory5 for weak complexes, A G ~ Tis given approximately by -* -+ --% p,(b2 t- a b S ) zz b2,u. ( 5) A/.iCT where pl = ($1 1 b/ *I) is the dipole moment of the dative structure. Applying the variation method to eq I one can ge! the following relation
aWo 4- bHo1
=:
WN(a 4- b S )
(6)
where WO = (ee\A/*o),Hon = (qfo\g\*l), S == ( q o / * l ) , and W N = ( \ k ~ l f i I \ I / ~N) -AN if QN is a normalized function and the reference energy of two separated solvated molecules is equal to 2 8 1 0 . ~ " ~ For weak complexes, a s 1, bS
