Structure of 7-methyl-8-azaadenine. A crystallographic and molecular orbital study

Abstract

The crystal and molecular structure of 7-methyl-8-azaadenine (6-amino-7-niethyl-8-azapurine), CzH6N6, has been determined from three-dimensional x-ray counter data obtained using Mo Ka radiation. The material crystallizes in the orthorhombic space group Pbcn with eight formula units in a cell of dimensions a = 7.578 (2), b = 13.328 (3), and c = 12.566 ( 4 ) A. The observed and calculated densities are 1 .57 (3) and 1.572 g cmW3, respectively. The structure has been refined to a final value of the conventional R factor (on F ) of 0.041 using 1 I25 independent intensities. The azapurine ring is approximately planar. w i t h no atom deviating from the least-squares plane by more than 0.03 A. There is considerable intermolecular hydrogen bonding in the crystals, involving N ( I ) and N(3) as acceptors and the amino group as the donor. I t is noteworthy that neither N(8) nor N ( 9 ) participate in hydrogen bonding. A C N D 0 / 2 molecular orbital calculation provides a n explanation for this observation b j showing that the residual negative charges on K( I ) and N(3) (-0.27 and -0.23 electron, respectively) are much larger than those on N(8) and N(9) (-0.01 and -0.16 electron, respectively).T h e 8-azapurines ( I ) , which a r e purines (11) in which the imidazole ring has been changed t o a 1,2,3-triazole, a r e of H

Theoretical study of the tautomerism of 8-azaadenine

“…Table 1 lists the gas-phase most relevant geometric parameters for the tautomers calculated here. The derived structural parameters compare well with those reported for 7-methylazaadenine 21 with rms deviations of ca 0.04 Å for the bond lengths and 1.2-5.2°for bond angles. The average N7-N8 and N8-N9 distances for all three tautomeric forms are 1.287 and 1.304 Å , i.e.…”

Intersystem Crossing to Excited Triplet State of Aza Analogues of Nucleic Acid Bases in Acetonitrile

“…Our calculation indicated that the S 0 state of all the aza analogues had a planar molecular structure as well as the corresponding normal bases. The molecule structures of 7-methyl-8-azaadenine, 8AA monohydrated, and 6AU were reported to be planar by the X-ray structure analysis.…”