Energetics of the singlet and triplet states of alkylnitrenium ions: ab initio molecular orbital calculations

Electronic Properties of Nitrenium Ions

“…However, in these calculations, it should be noted that the barriers to rearrangement are small À3.1 and 2.2 kcal/mol, respectively. Previous calculations at the MP4 level 22 and the CCSD(T) level 21 showed similar trends: one methyl substantially reduces DE st and additional one reduces further, but by a more modest amount. However, the MP4 and CCSD(T) calculations showed somewhat larger splittings.…”

“…There have been a number of computational studies, using various methodologies such as, DFT, coupled cluster, 21 and MP4, 22 directed at understanding the singlettriplet energy separation in these species. While quantitative agreement is still elusive, each method qualitatively agrees that the former effect predominates: electron donation from the alkyl substituent stabilizes the singlet relative to the situation in NH 2 þ .…”

Nitrenium Ions and Problem of Direct Electrophilic Amination of Aromatic Compounds

“…Up to now, quantum-chemical calculations were performed for a wide variety of nitrenium ions: NH 2 + [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], MeNH + [22,24,25,30,36,41], Me 2 N + [22,24,25,30,41], MeAcN + [22], (CH 2 ) 2 N + [42], (CH 2 ) 4 N + , (CH 2 ) 5 N + [22,24,25], (XCH=CH)MeN + (X = H, Cl) [25], (CH) 2 N + , CHN 2 + [43], (CH) 6 N + [44], XN 3 + (X = O, S, Se, Te) [45], XNH + (X = NH 2 , PH 2 , OR, SH, Cl, F, Br, I, CN, NC 2 ) [23,27,28,32,34,36,40,46], X(CHO)N + [X = N, NH 2 , PH 2 , OR, SH, Ph(CH 2 ) n O] …”

“…Unsubstituted nitrenium ion H 2 N + (3) exists mainly in the triplet state, and the energy difference between the singlet and triplet states was estimated at 89-152 kJ/mol [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. The best agreement with the experimental value (∆E ST = 125.9 kJ/mol [88]) was obtained by ab initio calculations (∆E ST = 125.8 kJ/mol, CASSCF-MRCI + ZPVE; ∆E ST = 125.6 kJ/mol, TZ2P(f,d)CASSCF(6,6)-SOCI + ZPVE [33] 149.4°0 .1025 nm 475 calculations [MP4(SDTQ)/6-311 + G(3d2f,2p)// MP2/6-311 + G(3d,2p)] showed that both singlet and triplet states of H 2 N + ion have an angular structure and that the HNH angle in the triplet state is considerably greater [24].…”

“…The best agreement with the experimental value (∆E ST = 125.9 kJ/mol [88]) was obtained by ab initio calculations (∆E ST = 125.8 kJ/mol, CASSCF-MRCI + ZPVE; ∆E ST = 125.6 kJ/mol, TZ2P(f,d)CASSCF(6,6)-SOCI + ZPVE [33] 149.4°0 .1025 nm 475 calculations [MP4(SDTQ)/6-311 + G(3d2f,2p)// MP2/6-311 + G(3d,2p)] showed that both singlet and triplet states of H 2 N + ion have an angular structure and that the HNH angle in the triplet state is considerably greater [24].…”