Chemical shifts and bond modification effects for some small first-row-atom molecules

Chemical shifts and shift changes with bond modification have been calculated for some small first-row-atom molecules employing a (6311/311/1)=[4s, 3p, d] heavy atom, (31)=[2s] hydrogen basis in the GIAO approach. Shifts and shift anisotropies using this intermediate size basis agree as well with experiment as other, more extensive basis sets; heavy atom shifts are determined reasonably well on an absolute basis and hydrogen shifts are acceptable on a relative scale. Nearly all shift first derivatives are negative with respect to bond lengthening as are the second derivative terms. These results suggest that in most cases a negative temperature coefficient for the chemical shifts of the heavy atoms will be observed, an effect which in fact does obtain in most cases known experimentally.