Least‐squares refinement of the crystal and molecular structures of DNA and RNA from X‐ray data and standard bond lengths and angles

tion, there are two other short contacts, namely N . . . O(1) (II0rI), 3.084 A and N . . . O(1), 2.752 A. The atom O(1) belongs to the same molecule while the atom O(1) (II0ia) lies approximately on the line C(2)-N. The arrangement of this latter type is very similar to that of carbonyl oxygen [O(1")] around the N H + group in valine hydrochloride (Parthasarathy, 1966) or in 7-glycine (Iitaka, 1961).