A 13C Solid-State NMR Investigation of the Alkynyl Carbon Chemical Shift Tensors for 2-Butyne-1,4-diol

Acetylenic Carbon-13 Chemical Shift Tensors for Diphenylacetylene and (η2-Diphenylacetylene)Pt(PPh3)2: A Solid-State NMR and Theoretical Study

“…The 13 C NMR spectra from a stationary powder sample of diphenylacetylene-α,β- 13 C 2 obtained at 4.7 and 9.4 T are shown in Figure ; Table summarizes the data derived from the 13 C spectral simulations. While the line shape seen in Figure C appears to be unusual for a dipolar chemical-shift spectrum, this pattern has been observed before and comes from a cancellation effect in the orientation dependence of the shielding and dipolar coupling interactions for one of the transitions. , The best-fit simulated spectra yield a value of R DD = 4025 ± 50 Hz corresponding to a length of 1.236(5) Å for the alkynyl bond. This NMR-derived bond length is ∼4% greater than the 1.192(4) Å measured via X-ray crystallography by Zanin et al Such an apparent lengthening is not unexpected as NMR-determined bond lengths are generally 1−4% larger than those measured by diffraction studies because of averaging from vibrational/librational motion. − The isotropic chemical shift measured from the spectrum of the sample under MAS conditions, δ iso = 89.8 ppm, is consistent with the previously reported solvated sample value of 89.6 ppm .…”

“…While the line shape seen in Figure 1C appears to be unusual for a dipolar chemical-shift spectrum, this pattern has been observed before and comes from a cancellation effect in the orientation dependence of the shielding and dipolar coupling interactions for one of the transitions. 26,47 The best-fit simulated spectra yield a value of R DD ) 4025 ( 50 Hz corresponding to a length of 1.236-(5) Å for the alkynyl bond. This NMR-derived bond length is ∼4% greater than the 1.192(4) Å measured via X-ray crystallography by Zanin et al 63 Such an apparent lengthening is not unexpected as NMR-determined bond lengths are generally 1-4% larger than those measured by diffraction studies because of averaging from vibrational/librational motion.…”

“…Alkynyl carbon CS tensors have previously been published for acetylene, , propyne, 2-butyne, , diacetylene, 2-butyne-1,4-diol, methoxyacetylene, propiolaldehyde, trimethylsilylacetylene, and phenylacetylene 28 (relaxation study). The CS tensor of DPA resembles that of the structurally similar phenylacetylene, whose terminal carbon has CS tensor components: δ 33 = −27.8 ppm and δ 11 = δ 22 = 131.8 ppm (values determined under the assumption that δ 11 = δ 22 ) .…”

“…An assortment of alkynyl carbon CS tensors have previously been reported for compounds with a variety of substituents on the acetylenic carbons. 19,[23][24][25][26][27][28] The alkynyl carbon CS tensor of DPA was reported during a preliminary investigation of DPA and PtDPA; 10 however, the presence of multiple solvate forms of PtDPA hindered completion of the study.…”

“…The current investigation of DPA, in conjunction with data from PtDPA, allows a complete picture of the changes that η 2 -bonding to platinum causes in the CS tensor of an alkynyl carbon. An assortment of alkynyl carbon CS tensors have previously been reported for compounds with a variety of substituents on the acetylenic carbons. ,− The alkynyl carbon CS tensor of DPA was reported during a preliminary investigation of DPA and PtDPA; however, the presence of multiple solvate forms of PtDPA hindered completion of the study.…”