Table 3. Experimental and Calculated ¹³C Isotropic Chemical Shifts (in ppm) for Phenobarbital Forms II and III^a.

	form IIa		form IIb		form IIc		form III
carbon	expt.	calc.	expt.	calc.	expt.	calc.	expt.	calc.
C1 – Carbonyl	147.15	147.53	148.91	149.43	147.15	147.80	149.01	149.00
C2 – Ispo	136.00	133.02	137.17	137.54	137.17	137.17	137.56	136.94
C3 – Quaternary	61.68	63.50	61.00	62.15	62.37	63.46	62.27	63.27
C4 – Methylene	30.35	33.78	32.21	36.10	27.22	28.74	27.12	28.63
C5 – Methyl	6.86	8.67	7.93	9.53	8.91	10.47	11.36	12.98
C6 – CO (edge)	177.41	179.70	169.87	171.61	173.20	175.19	174.20	176.89
C7 – CO	177.41	178.30	173.20	174.44	174.96	175.79	174.20	175.89
C8 – Ortho (edge)	125.76	125.02	127.02	127.10	125.40	124.93	127.57	128.12
C9 – Meta (edge)	131.39	131.12	130.18	130.72	133.74	134.39	130.70	130.29
C10 – Para	132.41	133.08	129.30	129.32	130.18	131.60	129.53	129.18
C11 – Meta	132.81	130.19	127.02	126.90	130.18	130.57	129.92	130.93
C12 – Ortho	129.70	131.72	127.02	128.20	125.76	126.52	127.57	128.26
RMSE		1.95		1.46		1.09		1.24

^aPredicted shieldings are reported for two-body fragment calculations using PBE0.