Differentiation between 6- and 7-Membered Rings Based on Theoretical Calculation of NMR Parameters

Table 5

Selected DFT-calculated three-bond heteronuclear ¹H-¹³C NMR spin-spin (scalar) coupling constants (³𝐽_H,C/Hz) ¹⁵N NMR chemical shifts (𝛿_N/ppm), and ¹⁷O NMR chemical shifts (𝛿_O/ppm) for 1 and 2.

Cmpd, conf.		H-2𝛼, C-9a	H-2𝛽, C-9a	H-3, C-5a	H-4𝛼,^a C-5a	H-4𝛽,^a C-5a	𝛿N5	𝛿O1	𝛿O3/4
	1	0.22	6.93	0.02	1.26	−0.03	−312.1	−1.6	−87.0
	2	6.41	0.35	4.30	−0.03	−0.18	−329.7	−3.2	−77.1
	3	6.76	0.16	5.64	0.02	−0.21	−317.1	−6.9	−77.2
1	4	6.59	−0.01	5.75	0.01	−0.20	−318.7	−6.3	−81.7
	5	7.06	0.24	5.39	−0.02	0.04	−313.4	−9.5	−75.2
	6	6.68	0.67	5.06	−0.01	−0.08	−310.6	−4.8	−68.5
	PWA	2.48	4.58	1.80	0.81	−0.07	−315.3	−3.0	−83.4
	1	1.00	0.36	−0.03	1.05	0.39	−324.3	−11.8	−61.5
2	2	4.28	7.17	−0.21	6.78	3.44	−322.3	0.9	−49.2
	3	6.56	3.89	−0.07	3.75	7.00	−315.6	−16.8	−43.3
	PWA	1.42	0.90	−0.04	1.50	0.83	−323.9	−11.3	−60.0

Legend: PWA, population-weighted average. ^aIn the case of 2; proR and proS, respectively, for 1.