steric effects on acyclic diaminocarbenes vs. their abnormal cyclic saturated and unsaturated analogues, at dft

we used dft calculations (m06/6-311++g^** level) to attain steric effects on the multiplicity, stability, and reactivity of acyclic diaminocarbene 1r and its saturated 2_r and unsaturated cyclic 3_r diaminocarbenes in normal and abnormal states. substituent groups are h, me, i-pr, t-bu. all optimized structures are stable singlet state. cyclization and aromaticity decrease nucleophilicity (n), proton affinity (pa) and increase the singlet–triplet energy gaps (δe_s-t) and homo-lumo energy gap (δe_h-l). in abnormals, δe_h-l, δe_s-t decrease and n increase than normal (except acyclic form).for better result on carbene properties, we used 3 series of isodesmic reactions that it is shown stability of carbene structures on cyclic and heterocyclic and unsaturated. it is determined that cyclic carbene stability increase with increase of substitution size. heteroatom in linear or acyclic structure causes carbene stability that this stability decrease with substitution size increase on heteroatom but in saturated and unsaturated cyclic structures, large substitution on heteroatom causes its corresponding carbene stability.