Table 2.

Bonding analyses for adenine—thymine small analogs A“T” and a“t”.^[a]

	A“T”	A“T” at R[sp3][b]			a“t′′	a”t′ at R[sp2][b]
Distances [Å]
N(H)⋅⋅⋅O	2.88	3.09			3.09	2.88
N⋅⋅⋅(H)N	2.90	3.14			3.14	2.90
Bond energy [kcal mol−1]
ΔE	−16.1	−14.4			−8.2	−6.7
ΔEprep	1.8	1.8			0.7	0.7
ΔEint	−17.9	−16.2			−8.9	−7.4
ΔEPauli	32.3	15.0			16.4	34.3
ΔVelstat	−28.4	−18.5			−14.4	−23.8
ΔEdisp	−3.4	−2.7			−3.4	−4.2
ΔEoi	−18.5	−10.0			−7.5	−13.7
ΔEσ	−16.6	−8.9
ΔEπ	−1.9	−1.1
Gross populations: N(H)⋅⋅⋅O [e−]
σLUMO+1 of A“	0.02	0.02		LUMO+1 of a”	0.01	0.01
σLUMO of A“	0.01	0.01		LUMO of a”	0.01	0.02
σHOMO of T“	1.95	1.97		HOMO of t”	2.00	2.00
σHOMO−1 of T“	2.00	2.00		HOMO−1 of t”	1.98	1.96
Gross populations: N⋅⋅⋅(H)N [e−]
σLUMO+1 of T“	0.04	0.03		LUMO+1 of t”	0.02	0.02
σLUMO of T“	0.03	0.02		LUMO of t”	0.01	0.01
σHOMO of A“	1.91	1.94		HOMO of a”	1.95	1.93
σHOMO−1 of A“	2.00	2.00		HOMO−1 of a”	1.99	1.99
Orbital energies of A“ [eV]				Orbital energies of a” [eV]
σLUMO+1	0.29			LUMO+1	0.30
σLUMO	−0.39			LUMO	−0.24
σHOMO	−5.80			HOMO	−5.31
σHOMO−1	−10.86			HOMO−1	−5.60
Orbital energies of T“ [eV]				Orbital energies of t” [eV]
σLUMO+1	0.18			LUMO+1	0.41
σLUMO	−0.64			LUMO	−0.49
σHOMO	−5.85			HOMO	−5.77
σHOMO−1	−9.80			HOMO−1	−6.54
Overlap < Α“|Τ” > for N(H)⋅⋅⋅O				Overlap < a“|t” > for N(H)⋅⋅⋅O
<σLUMO+1|σHOMO>	0.11	−0.10		<LUMO+1|HOMO−1>	−0.08	−0.08
<σLUMO|σHOMO>	0.09	−0.08		<LUMO|HOMO−1>	−0.12	−0.11
Overlap < Α“|Τ” > for N⋅⋅⋅(H)N				Overlap < a“|t” > for N⋅⋅⋅(H)N
<σHOMO|σLUMO+1>	0.27	0.26		<HOMO|LUMO+1>	−0.15	0.14
<σHOMO|σLUMO>	0.23	0.21		<HOMO|LUMO>	0.10	−0.10

[a] Energies and geometries computed at BLYP-D3(BJ)/TZ2P level of theory: A“T” in C_s symmetry, and a“t” in C₁ symmetry (chair conformation). [b] A“T” has been elongated to the distance of a“t”, R(sp³), and a“t” compressed to the distance of A“T”, R(sp²).