Structures of pyridine and quinoline-n-oxides

~e~ar~rn~~t of

Chemistry, Denton,

(Ree*~ived in IKA 24 June 1970; There have been few reparts aromatic

ring

analyses

have been completed

North Texas State Texas

76203

received

in uic for

in the literature

compounds containing

bond.

an two such compounds,

Z-hydro~~etby~~~r~dine-~-oxide

(II]

x-ray

data

the

structural

Three dimensional

lvt97Dj

propertiesof x-ray

structural

8-hydrox~uinoliue-~-oxide (I), and

in an attempt

to provide

such infornratian.

(II)

CT.1 The preliminary

~~~bli~~t~*n 7 July

concerning

the N-Q dative

University

are:

crystal symmetry

space

moIec~os

group

per cell

III

monoclinic

P2,/c

4

12.136

4.921

13.138

-0.3576

U-I)

monoclinic

P2I/C

4

7.079

8.946

10.599

-0.2254

a

b

C

CbSS

Botk structureswere solved by a direct phasing proceduredue to Long (I) and were refined by full matrix are 0.053

least

squares

and 0.111,

techniques.

The final residual factors (R) for (I) and (II)

These are

respectively.

two features

of

interest

in the structures.

The N-O bond distancesare 1.333(Z)i and X.332 i for (I) and (II), respectively. These are in good agreementwith N-O distancesreportedfor sin&tarmqmmds pyridine-N-oxide both

structures

In (I), length

(23,

is

1.42 i.

and X,X!& i in tetrafpyridine oxide~cop~r(II)pa~hlorate(3). Also,

exhibit

the hydrogen

sach as I.33 i in

hydrogen

bonding:

band is between In (II],

intramolecular

the bydroxyf

the hydroxyl

hydrogen SW5

in

hydrogen atom is

(I) and inttwmolecularin (II), and the dative

oxygen;

bonded to an M-oxide

its

oxygen

atom

3204

$10. 57

of a neighboring,symmetryrelated molecule. Its length is 1.99 i. These data appear to support a correlationbetween the strengthof the hydrogenbonding and the length of the N-O bond as proposedby Hanson (4) and Hanson and Hum1 (5) in

their studies of the compounds,

myxin and iodinin;that is, as the hydrogenbond to the N-oxide is strengthened,the N-O distance is lengthened. This effect is attributedto the delocalizationof the nonbonding electronson the oxygen atom affectedby hydrogenbonding which results in a decrease in the ionic characterof the N-O bond. The N-O distancesin myxin and iodinin are 1.32 and 1.31 i, respectively,when the N-oxide oxygen atoms are affectedby intramolecularhydrogen bonding. However, the additiona N-O bond in myxin is unaffectedby hydrogenbonding and its distance is given as 1.28 i.

Other featuresof these two structuresappear to be normal: the pyri-

dine and quinolinemoietiesare planar within experimentalerror and bond distancesand angles are as expectedfor these two types af aromatic systems. Acknowledgements:We wish to thank the Oak Ridge National Laboratoryfor the use of its facilities. We are gratefulfor supportby grants from the Robert A. Welch Foundationand the North Texas State UniversityFaculty ResearchFund.

References: (1) R. E. Long, DoctoralDissertation,Departmentof Chemistry,Universityof California, Los Angeles, 1965. (2) J. C. Morrow, U. Dincer,and B. P. Huddle, American Crystallographic Association, Winter Meeting Abstracts,March, 1970. (3) J. D. Lee, D. S. Brown, and B. G. A, Melsom, Acta Cryst.,825, 1378, (1969). (4) A. W. Hanson, Acta Cryst.,E,

1084, (1968).

(5) A. W. Hanson and K. Huml, Acta Cryst.,E,

1766, (1969).