Rotational Spectroscopy of 1-Cyano-2-methylenecyclopropane (C₅H₅N)─A Newly Synthesized Pyridine Isomer

Abstract

The gas-phase rotational spectrum of 1-cyano-2methylenecyclopropane (C 1 , C 5 H 5 N), an isomer of pyridine, is presented for the first time, covering the range from 235 to 500 GHz. Over 3600 a-, b-, and c-type transitions for the ground vibrational state have been assigned, measured, and least-squares fit to partial-octic A-and S-reduced distorted-rotor Hamiltonians with low statistical uncertainty (σ fit = 42 kHz). Transitions for the two lowest-energy fundamental states (ν 27 and ν 26 ) and the lowestenergy overtone (2ν 27 ) have been similarly measured, assigned, and least-squares fit to single-state Hamiltonians. Computed vibration−rotation interaction constants (B 0 −B v ) using the B3LYP and MP2 levels of theory are compared with the corresponding experimental values. Based upon our preliminary analysis, the next few vibrationally excited states form one or more complex polyads of interacting states via Coriolis and anharmonic coupling. The spectroscopic constants and transition frequencies presented here form the foundation for both future laboratory spectroscopy and astronomical searches for 1-cyano-2-methylenecyclopropane.

Photoisomerization of (Cyanomethylene)cyclopropane (C5H5N) to 1-Cyano-2-methylenecyclopropane in an Argon Matrix

“…The authentic IR spectrum of 7 (Figure c) matches that of the photoproduct and also that of the computational prediction, unambiguously establishing the assignment of 7 as the photoproduct. Obtaining a sample of 7 also allowed us to measure the laboratory rotational spectrum of this speciesan additional pyridine isomer, which is reported in a companion manuscript …”

“…Compound 5 has been identified previously, − but compound 7 is presented for the first time in this work. The synthesis and spectroscopic investigation of these species are part of a long-standing pursuit by this group of the chemistry and spectroscopy of the pyridine isomers shown in Figure . ,− …”

“…C 5 H 5 N isomers that have been studied by rotational spectroscopy: ( E )-1-cyano-1,3-butadiene ( E -1 ), , ( Z )-1-cyano-1,3-butadiene ( Z -1 ), , 4-cyano-1,2-butadiene ( 2 ), , 2-cyano-1,3-butadiene ( 3 ), 4-cyano-1-butyne ( 4 ), (cyanomethylene)­cyclopropane ( 5 ), 1-cyanocyclobutene ( 6 ), 1-cyano-2-methylenecyclopropane ( 7 ), and pyridine ( 8 ) …”

A Tale of Two Tails: Rotational Spectroscopy of N-Ethyl Maleimide and N-Ethyl Succinimide

“…The agreement between the calculated and the experimental rotational constants is excellent (<0.09%). To convert the quartic distortion constants from the III r representation reported in the Gaussian output to the I r representation, we used the τ centrifugal distortion constants from our anharmonic calculations. The agreement between the experimental quartic centrifugal distortion constants and calculated values is ∼15%, which is typical for these constants.…”