Accurate Spectroscopic Constants for the Ground Vibrational State of Methyl Isocyanide-d3, CD3NC

✍ Scribed by W.A. Burns; K.R. Leopold; Alexander D. de Winter; Mark D. Marshall

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 78 KB
• Volume: 181
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1996.7165

✦ Synopsis

NOTE

Accurate Spectroscopic Constants for the Ground Vibrational State of Methyl Isocyanide-d 3 , CD 3 NC Recently, a detailed investigation of the infrared spectrum of methyl 6 M potassium cyanide were added, and the mixture was left undisturbed for 24 hr. The resulting solution was decanted into a round-bottom flask isocyanide, CH 3 NC, has been reported by Bernheim and co-workers (1-6). At Amherst College, we have sought to extend this work to the fully and distilled. The fraction removed at 55 -60ЊC was collected and stored at dry-ice temperatures until it was needed. We note that this procedure deuterated form of the molecule, CD 3 NC (7). However, our analysis has been hampered by a lack of spectroscopic constants for the ground vibra-was used to successfully synthesize CD 3 NC on three separate occasions.

However, at one point the resulting CD 3 NC exploded while being trans-tional state which are of sufficient accuracy and precision to allow the confident use of combination differences in assigning our infrared spectra ferred between vessels. This occurred when a sample of CD 3 NC was warmed to above 080ЊC, and the vapor recondensed through a short in the 10-mm region. In particular, the only published microwave spectrum for the molecule consists of two low-J rotational transitions, with fully tube into a liquid-nitrogen-cooled metallic vessel. Interestingly, Clothier et al. (15) have reported an explosion of liquid methyl isocyanide at resolved K structure but no reported value for the D J centrifugal distortion constant (8). Thus, we report here the observation and analysis of high room temperature.

Thirty-five transitions were observed which have been attributed to the resolution, pure rotational transitions near 11.5 cm 01 (JЉ Å 18-21) for CD 3 NC. This has allowed accurate determination of ground vibrational state ground state of CD 3 NC, and a typical transition is reproduced in Fig. 1.

Each line was measured at least twice, and frequencies were reproducible spectroscopic constants which will be useful in the assignment of the 10mm vibrational spectrum.

to within {0.5 MHz. The spectrum showed the characteristic K structure of a symmetric top with a positive value of D JK , and line intensities were The moderately high-J levels of CD 3 NC have been observed using a tunable far-infrared spectrometer at the University of Minnesota. Details of found to decrease with increasing K, as expected for a prolate symmetric top. Due to the overlap of the K Å 0 and K Å 1 lines, only 29 of the 35 the spectrometer are given elsewhere (9-12). The sample cell consisted of a 28-in.-long, 1.25-in.-diameter cylindrical glass tube, with high density observed transition frequencies could be used in the determination of the pertinent spectroscopic constants. polyethylene windows. Spectra were observed at room temperature and with a pressure of CD 3 NC of between 150 and 225 mTorr.

The frequencies were analyzed using a least squares fit to the standard expression CD 3 NC was produced using a modified version of the technique presented in Organic Syntheses (13, 14). Briefly, 13.4 g of silver cyanide (AgCN) and 7.5 g of deuterated methyl iodide (CD 3 I) were allowed to react at 77ЊC for 6 hr in a sealed bomb reactor. Upon cooling, 75 ml of n Å 2B(JЉ / 1) 0 4D J (JЉ / 1) 3 0 2D JK (JЉ / 1)K 2 , [1]

FIG. 1 The J Å 20 R 19, K Å 5 transition of CD 3 NC.