%0 Journal Article %A Bettinger, Holger F. %A Sander, Wolfram %D 2003 %T Dehydrophenylnitrenes:  Quartet versus Doublet States %U https://acs.figshare.com/articles/journal_contribution/Dehydrophenylnitrenes_Quartet_versus_Doublet_States/3647826 %R 10.1021/ja029296u.s001 %2 https://ndownloader.figshare.com/files/5736684 %K 2 B 1 states %K 1 kcal mol %K MRCI %K 3.5 kcal mol %K quartet states %K CASSCF %K C 3. %K Doublet States %K 62 kcal mol %K MCQDPT treatment %K 1 state %K doublet state %K 22 kcal mol %K quartet ground state %K excitation energy %K 2 B 2 %K 32 kcal mol %K 2 B 2 state %K adiabatic excitation energies %X The geometries and energies of 4-, 3-, and 2-dehydrophenylnitrenes (3, 4, and 5) are investigated using complete active space self-consistent field (CASSCF), multiconfiguration quasi-degenerate second-order perturbation (MCQDPT), and internally contracted multiconfiguration−reference configuration interaction (MRCI) theories in conjunction with a correlation consistent triple-ζ basis set. 4-Dehydrophenylnitrene 3 has a quartet ground state (4A2). The adiabatic excitation energies to the 2A2, 2B2, 2A1, and 2B1 states are 5, 21, 34, and 62 kcal mol-1, respectively. The 2B2 state has pronounced closed-shell carbene/iminyl radical character, while the lowest-energy 2B1 state is a combination of a planar allene and a 2-iminylpropa-1,3-diyl. The MCQDPT treatment overestimates the excitation energy to 2B2 significantly as compared to CASSCF and MRCI+Q. Among quartet states, 4A2-3 is the most stable one, while those of 4 and 5 (both 4A‘ ‘) are 3 and 1 kcal mol-1 higher in energy. 5 also has a quartet ground state and a 2A‘ ‘ state 7 kcal mol-1 higher in energy. On the other hand, the doublet-quartet energy splitting is −6 kcal mol-1 for 4 in favor of the doublet state (2A‘ ‘). Hence, 2A‘ ‘-4 is the most stable dehydrophenylnitrene, 3.5 kcal mol-1 below 4A2 of 3. The geometry of 2A‘ ‘-4 shows the characteristic features of through-bond interaction between the in-plane molecular orbitals at N and at C3. The 2A‘ state of 4 resembles the 2A1 state of 3 and lies 32 kcal mol-1 above 4A‘ ‘-4. The lowest-energy 2A‘ state of 5, on the other hand, resembles the 2B2 state of 3 and lies 22 kcal mol-1 above 4A‘ ‘-5. %I ACS Publications