Table 2.

Descriptors for HBS types found in barbiturates: short HBS symbol [19] and number of o- and t-connections [N _o, N _t]

Type	Short HBS symbol	[N o, N t]	[N o, N t]A [N o, N t]B …	Pbtl form(s)
C-1	C42[0]	[0, 2]		X
C-2	C42[0]	[0, 2]		I, II, III
C-3	C44[33.42.5]	[4, 0]		V
C-4	C43[42.6]	[2, 1]
C-5	C54.32[(53.62.7)(5)]	[2, 1]	[3, 1][1, 1]	VI
L-1	L43[63-hcb]	[2, 1]
L-2	L44[44.62-sql]	[4, 0]
L-3	L64.22[(64.8.10)(6)]	[2, 1]	[2, 2][2, 0]	I, II
L-4	L43[63-hcb]	[2, 1]
L-5	L43[63-hcb]	[2, 1]
L-6	L32.54.43[(10)(63.103)(63)]	[2, 1]	[1, 1][3, 1][2, 1]
F-1	F44[66-dia]	[4, 0]
F-2	F43[103-ths]	[2, 1]

For graphical representations, see Fig. 2 and Ref. [23]