Acetylenes
		Deuterium
	Nuclear Quadrupole Coupling Constants
		in the Acetylenes
	Calculated and experimental deuterium nqcc's in acetylene and the acetylene derivatives HCCX are collected in Table 1.  The calculated nqcc's are consistently 4-5 % larger than the experimental values.  Bond lengths in the HCC moiety are shown in Table 2.
	Table 1. Deuterium nqcc's in HCCX (kHz).   Molecule Calc. Expt. Ref.   HCCH 214.5 208.5(9)   [1] HCC-CCH 216.6 206.1(4)   [2] HCCF 218.9(20) * 210.9(14)   [3] 205.4(12)   [4] 212(10)   [5] HCCCl 217.2 208.5(15)   [6] 207.0(28)   [7] HCCBr 216.7 207.7(18)   [4] HCCCN 211.8 203.43(52)   [8]   198.2(46)   [9]   228.8(55) [10] HCCNC 215.1 206.7(10) [11] HCCCH3 218.3(13) * 208(10)   [5]   228(2) [12] HCCCF3 212.3 201.9(53) [13] HCCC6H5 212.2 ** 207.6(10) *** [29]
	* The estimated uncertainties in the calculated nqcc's for HCCF and HCCCH3 are due only to the (relatively large) uncertainties in the HC bond lengths (see Table 2).
	** ETA = 0.005     *** ETA = - 0.001
	Table 2. Bond lengths in the HCC moiety in HCCX (Å).       HC     CC Type Ref.   HCCH 1.06215(17) 1.20257(9) re [14]   1.0625(1) 1.2024(1) re [15] HCC-CCH 1.0609 1.2104 est. re   [2] HCCF 1.0603(15) 1.1962(8) re [16]   1.0591(5) 1.1961(2) re [17] HCCCl 1.0605 1.2030(5) re [18]   1.0604 1.2032 rmrho [19] HCCBr 1.0608(0) 1.2036(1) rmrho [20] HCCCN 1.0624(5) 1.2058(5) re [21] HCCNC 1.0610 1.2032 re [22] HCCCH3 1.061(1) 1.204(1) re [23] HCCC6H5 1.0654 1.2073 ropt* Here
	* B3P86/6-31G(3d,3p) optimization.
	Trifluoromethyl Acetylene (3,3,3-Trifluoropropyne)
	Cox et al. [13] derived a zero-point average (rz) structure in which the HC bond length is 1.051 Å.  This result is similar to the rs bond lengths in HCCF (1.053 Å, [24]), HCCCl (1.055 Å [25,19]), HCCBr (1.055 Å [26]), and HCCNC (1.055 Å [27]), all of which are short compared with the equilibrium bond lengths.
	Therefore, calculation of the HC bond length was made following the procedure of Demaison and Wlodarczak [28], who have shown that ab initio optimizations are reliable for calculation of the equilibrium CH bond length, if an empirical correction is made.  Here, B3LYP/6-31+G(df,3pd) optimization was made of the structures of HCCH, HCCCl, HCCBr, HCCCN, HCCNC, and HCCCH3.  Linear regression analysis of the calculated versus equilibrium HC and CC bond lengths gives the following relationships:
			r(HC) = 1.0213 ropt(HC) - 0.0230,
			r(CC) = 0.6597 ropt(CC) + 0.4089.
	The residual standard deviations are 0.0001 Å and 0.0005 Å, respectively.  These relationships give r(HC) = 1.0624 Å and r(CC) = 1.2011 Å, which agrees with the rz value of 1.2012(8) Å.  And so, the nqcc given in Table 1 is that calculated on the rz structure, but with r(HC) = 1.0624 Å.
	Comment
	The calculated (rigid molecule) nqcc's are consistently about 4-5 % larger than the experimental values.  Sutter and Dreizler [3] in the case of fluoroacetylene, and Spahn et al. [8] in the case of cyanoacetylene have shown that this difference can be accounted for by the effects of vibrational averaging on the efg seen by the deuterium nucleus.
	[1] R.L.DeLeon and J.S.Muenter, J.Mol.Spectrosc. 126,13(1987); J.Chem.Phys. 72,6020(1980). [2] K.Matsumura, R.D.Suenram, F.J.Lovas, and T.Tanaka, J.Mol.Spectrosc. (2006). [3] D.H.Sutter and H.Dreizler, Z.Naturforsch. 56a,425(2001). [4] N.Heineking, M.Andolfatto, C.Kruse, W.Eberstein, and H.Dreizler, Z.Naturforsch. 43a,755(1988). [5] V.W.Weiss and W.H.Flygare, J.Chem.Phys. 45,8(1966). [6] L.M.Tack and S.G.Kukolich, J.Mol.Spectrosc. 94,95(1982). [7] N.Heineking, M.Andolfatto, U.Keussen, A.Mues, and H.Dreizler, Z.Naturforsch. 44a,735(1989). [8] H.Spahn, H.S.P.Müller, T.F.Giesen, J.-U.Grabow, M.E.Harding, J.Gauss, and S.Schlemmer, Chem.Phys. xxx,xxx(2008). [9] W.H.Stolze and D.H.Sutter, Z.Naturforsch. 39a,1092(1984). [10] E.Fliege, H.Dreizler, and B.Kleibömer, J.Mol.Struct. 97,225(1983). [11] M.Krüger, W.Stahl, and H.Dreizler, J.Mol.Spectrosc. 158,298 (1992). [12] C.D.Cogley, L.M.Tack, and S.G.Kukolich, J.Chem.Phys. 76,5669 (1982). [13] A.P.Cox, M.C.Ellis, A.C.Legon, and A.Wallwork, J.Chem.Soc. Faraday Trans. 89,2937(1993). [14] A.Baldacci, S.Ghersetti, S.C.Hurlock, and K.N.Rao, J.Mol. Spectrosc. 59,116(1976). [15] E.Kostyk and H.L.Welsh, Can.J.Phys. 58,912(1980). [16] A.F.Borro, I.M.Mills, and A.Mose, Chem.Phys. 190,363(1995). [17] P.Botschwina and S.Seeger, J.Mol.Struct. 320,243(1994). P.Botschwina, M.Oswald, J.Flügge, A.Heyl, and R.Oswald, Chem. Phys.Lett. 209,117(1993). [18] M.Horn, P.Botschwina, and J.Flügge, J.Chem.Soc. Faraday Trans. 89,3669(1993). [19] M.LeGuennec, G.Wlodarczak, J.Demaison, H.Bürger, and O.Polanz, J.Mol.Spectrosc. 158,357(1993). [20] R.J.Berry and M.D.Harmony, Struct.Chem. 1,49(1989). [21] P.Botschwina, M.Horn, S.Seeger, and J.Flügge, Mol.Phys. 78,191 (1993). [22] P.Botschwina, M.Horn, S.Seeger, and J.Flügge, Chem.Phys.Lett. 195,427(1992). [23] M.LeGuennec, J.Demaison, G.Wlodarczak, and C.J.Marsden, J.Mol.Spectrosc. 160,471(1993). [24] J.K.Tyler and J.Sheridan, Trans. Faraday Soc. 59,2661(1963). [25] H.Jones, M.Takami, and J.Sheridan, Z.Naturforsch. 33a,156(1978). [26] H.Jones, J.Sheridan, and O.C.Stiefvater, Z.Naturforsch. 32a,866 (1977). [27] M.Krüger, H.Dreizler, D.Preugschat, and D.Lentz, Angew.Chem. Int.Ed.Engl. 30, 1644(1991). [28] J.Demaison and G.Wlodarczak, Struct.Chem. 5,57(1994). [29] H.Driezler, H.D.Rudolph, and B.Hartke, J.Mol.Struct. 698,1(2004).
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	Molecules/Deuterium
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