Conformational stability, barriers to internal rotation of 2-aminothiophenol (d0 and d3): A combined vibrational and theoretical approach

Infrared, Raman and NMR spectra, conformational stability, normal coordinate analysis and B3LYP calculations of 5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1-carbothioamide

“…As reported by NIST (http://srdata.nist.gov), an NH 2 barrier to internal rotation of 10.99 kcal/mol (3844 cm À1 ) was obtained for acetamide (CH 3 CONH 2 ) which compares to the 10.4-19.2 kcal/mol (3637-6715 cm À1 ) calculated herein for AMPC. These values are also in good agreement with a range of 10.0-18.2 kcal/mol (3498-6366 cm À1 ) recorded earlier for 2AP [41], 2ATP [42] and adenine [43]. These barriers reflect the small size of the OH in 2AP and the C@O group in acetamide compared to the larger size of SH in 2ATP and C@S moiety in AMPC.…”

“…Four A 0 NH 2 bending modes are predicted at 1632 (m 9 ), 1593 (m 10 ), 1181 (m 19 ), and 916 (m 23 ) cm À1 , Table 1. Therefore, the unscaled NH 2 scissor modes, m 9 at 1632 and t 10 at 1593 cm À1 were consistent with very strong IR bands recorded at 1601 and 1558 cm À1 , respectively in agreement with those reported earlier [41][42][43]69]. On the other hand, the 1558 cm À1 band seems to be coincident with the C@N stretching mode (m 11 ).…”

“…The NH 2 scissoring frequency is in the spectral range 1950-1650 cm À1 as reported for aniline [68], 2-aminophenol [41], 2-aminothiophenol [42], and adenine [43]. Four A 0 NH 2 bending modes are predicted at 1632 (m 9 ), 1593 (m 10 ), 1181 (m 19 ), and 916 (m 23 ) cm À1 , Table 1.…”

“…The calculated SPs (Table 2) for AMPC reveal CAN distances for C 1 AN 7 and C 6 AN 13 that are shorter than those reported for AP (1.429 Å), ATP (1.370 Å) and adenine (1.357 Å) by $0.029-0.109 Å [41][42][43], highlighting the double-bond character of these bonds (for atom numbering see Fig. 7).…”

“…Therefore, a thorough Raman, IR and NMR spectroscopic investigation is reported here complemented by B3LYP theoretical predictions [20][21][22][23][24] with bases sets up to 6-31++G(d,p) to provide novel insight on vibrational assignments and conformational stability of AMPC. Complimentary to our studies on barriers to internal rotations of methyl [37][38][39][40] and NH 2 [41][42][43] rotors, potential surface scans (PSS) of the CH 3 , CH 3 S and NH 2 groups were undertaken to shed light on the rather complicated conformational interchanges in the molecule under investigation.…”