An Assessment of Alternative Low Level Calculation Methods for the Initial Selection of Conformers of Diastereomeric Esters

Table 1

Correlation of conformer energies resulted from minimization with LLMs (Steps 1 and 2, Figure 2) with single point energies calculated for the geometries optimized with LLMs by using high level RefM1 (Step 3, Figure 2).

Parameter^a	UFF^b	Dreiding^b	AM1^b	PM3^b	PM6	MM3^b	MM+^b
𝑅^2	0.76	0.14	0.60	0.04	0.436	0.89	0.65
RMS (kcal/mol)	4.17	5.38	3.80	7.31	3.54	2.78	3.32
Slope	1.17	0.24	0.46	0.04	0.49	1.12	0.56
Intercept	0.38	2.31	0.49	1.64	1.91	−0.15	1.42

^a𝑅²-correlation coefficient.
RMS-root mean square deviation of the energy values.
Slope and intercept characterized systematic deviation of the correlated energy values.
Ideally they should be 1.00 and 0.00, respectively.
^bCorrelation diagrams are presented in Figures 3–8.