Laboratory Detection of the Ring‐Chain Carbenes HC₄N and HC₆N

Abstract

The highly polar ring-chain carbenes and formed by substituting either CN or CCCN HC 4 N HC 6 N, for a hydrogen atom in cyclopropenylidene were detected in a supersonic molecular beam with (c-C 3 H 2 ), a Fourier transform microwave spectrometer. Seven a-and four b-type rotational transitions of HC 4 N and 11 a-type transitions of each with resolved nitrogen nuclear quadrupole hyperÐne structure, HC 6 N, were measured between 6 and 21 GHz, yielding precise values for the three rotational constants, the leading centrifugal distortion constants, and the quadrupole coupling constants. Like the hydrocarbon carbenes and both new molecules have a planar ring-chain structures and singlet C 5 H 2 , C 7 H 2 , C 9 H 2 , electronic ground states. The strongest lines of can be detected with a signal-to-noise ratio HC 4 N exceeding 10 in a total integration time of less than 1 s, but the lines of were nearly 100 times HC 6 N weaker.

Rotational spectroscopy, dipole moment and 14N nuclear hyperfine structure of iso-propyl cyanide

“…The situation for cyanoketene, v z % À3.94 MHz [41], is uncertain not only because of the large error bar, but also because small deviations from the assumed position of the z-axis may have a substantial effect on the v x and v z values because the CN bond is bent far away from all axes. Cyanocyclopropenylidene, in which the z-axis essentially agrees with the a-axis, and thus v z = À4.495 MHz [42], and hydrogen cyanide, v z = À4.7078 MHz [43], have larger values. Similarly, a value of À4.61 MHz has been inferred for acetyl cyanide aided by quantum chemical calculations [44].…”

Energetic and spectroscopic properties of the low-lying C7H2 isomers: a high-level ab initio perspective

“…On the contrary, the a-type transitions appear to be less sensitive to the angle of the chains with respect to the ring and therefore they can be predicted with greater accuracy than the b-type transitions. 35 Moreover, we also speculate that 3 can undergo Bergman cyclization 106 and would become 4.…”

“…This means that there is only one type of rotational transition possible for 3, which in part explains why it would be somewhat difficult to identify this molecule in comparison with 2, where both a-type and b-type rotational transitions are possible. 60 In fact, while analyzing the isoelectronic HC 6 N species, 35 McCarthy and co-workers had pointed out that only b-type rotational transitions are possible for 3. On the contrary, the a-type transitions appear to be less sensitive to the angle of the chains with respect to the ring and therefore they can be predicted with greater accuracy than the b-type transitions.…”

Commission 14: Atomic and Molecular Data: (Donnees Atomiques et Moleculaires)

“…This has changed with the radioastronomical detection of HCnN by Bell et al (1997). The CfA group led by P. Thaddeus has been very productive in the last three years in finding new spectra of carbon-chain molecules both in the laboratory (e.g., McCarthy et al 1997McCarthy et al , 1998McCarthy et al , 1999 and in space. New laboratory spectra include those of HC" (n=7,8,9,ll), HC 2 "+iN (n=5,6,7,8), carbon ring chains H 2 C 2 "+i (n=2, 3,4) and H 2 C 2n N (n-2,3), SiC" (n=3, 5,6,7,8) and many more.…”