DIPOLEMOMENTS AND STRUCTURES OF SEMICYCLIC IMIDES
Feb. 20, 1962
here; as the carbonyl group conjugates less with the ring nitrogen, it can conjugate more with the benzene ring so the extinction of this band increases. These data show how a methylene group can have a large effect on the conformation, dipole moment and ultraviolet spectra of semicyclic imides. Experimental All dipole moments were measured in dioxane a t 30" and calculations were made using the equation and method of
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Halverstadt and K ~ m 1 e r . l ~We wish to thank Dr. H. K. Hall, Jr., of du Pont for providing the compounds.6 We wish to thank Mr. M . K . Hrenoff of the Spectrographic Laboratory for all spectrographic measurements. Infrared spectra were run on a Perkin-Elmer model 21 in KBr disks 1:250, 0.6 mrn. thick. Ultraviolet spectra were run on a Cary model 11 or model 14 in ethanol in concentrations of 2.5 mg. %. (14) I . F. Halverstadt and W. D. Kumler, J. A m . Chcm. SOC.,64, 2933 (1942). (15) H . K. Hall, Jr., M. K . Brandt and R . hf. Mason, i b i d . , 80, 6420, 6424 (1958).
[CONTRIBUTION FROM THE DEPARTMENT OF PHARMACEUTICAL CHEMISTRY, SCHOOL OF PHARMACY, UNIVERSITY OF CALIFORNIA, SANFRANCISCO MEDICALCENTER, S A N FRANCISCO, CALIF. ]
The Dipole Moment and Structure of the Imide Group. 111. Straight Chain Imides >N-H O=C< Hydrogen Bonding and a Case of \C-H O=C( Hydrogen Bonding OH
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B Y CALVINM. LEE'
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w. D. KUMLER
RECEIVED JULY 31, 1961 Table I gives the dipole moments for N-methyldiacetamide (I),diacetamide (11) and N-methyldiformamide (111). Compound I has the expmted moment for the cis-trans conformation of imides; its moment varies only slightly (A0.2 D.) in going from dioxane to benzene to heptane; 11, while having the expected moment for the cis-trans conformation in dioxane, has a much lower moment in benzene (A1.0 D.) and heptane (A1.6 D.), suggesting hydrogen bonding in a cyclic dimer of low moment. Examination of physical properties and infrared frequency shifts substantiate this concIusion. The low moment of I11 also suggests hydrogen bonding in a cyclic dimer of low moment. The only possibility for hydrogen bonding is with the hydrogen attached to the amide carbon. We propose that N-methyldiformamide (111) forms a cyclic dimer (Fig. 4) with >C-H . O=C bonding. Theoretical considerations, examination of physical properties and molecular 0 ' weight determinations support the proposed dimer. Infrared studies of the >C=O stretching frequency show a greater shift to lower frequency (from solution to pure liquid) for I11 than for I which cannot hydrogen bond. INuclear magnetic resonance studies on I11 show the usual H-bond shift to higher field from the pure liquid to CC1, solution (17 C.P.S.a t 60 mc.). Calculations based on this shift indicate about 2.2 kcal./mole is involved in holding the dimer together.
