Table . Selected geometric parameters of NBD, NBN, NBA and QC in gas phase.* ,f *The B3LYP/aug-cc-pVTZ method. The total energy of NBA is given by -274.065626 Eh. # Rn are the ring perimeters R3, R3', R5||, R5| and R6. The numbers in (n1n2n3n4n5n6) are the carbon labels on the respective rings, which are given on the structure of NBN in Figure . a The NBD experimental ∠ (174) is measured from 91.90° of MW to 92.2° from ED and 92.5° by XSCD . The calculated angle at 91.98° is in close agreement with 92.327° and 91.977°, respectively using MP2/TAVP and B3LYP/TZVP models in our early study . b NBN 32 . Here ∠(174)° of NBN is 92.3° using single crystal X-ray analysis . c NBA . d The present study is reoptimized from the result of G4 calculations of Rablen . e QC gas electron diffraction (GED) . QC the angle of ∠(174) is 100° and ∠(216) is 60° as given . f C-C single bond length using the same B3LYP/aug-cc-pVTZ method is given by 1.528 Ǻ for propane. The measured C-C bond length of ethane (CH3-CH3) is 1.522 ± 0.02 Ǻ .