Table 2 Descriptors for HBS types found in barbiturates: short HBS symbol [19] and number of o- and t-connections [N _o, N _t]

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]