Robert E. Penn

HD structural isotope effect in hydrogen-bonded 2-aminoethanol

The microwave spectra of the d3 species of intramolecularly hydrogen-bonded 2-aminoethanol (ODCH2CH2ND2) as well as the d3-O18, d3-N15 and three d2 isotopic forms have been studied. The rs O-(D)⋯N distance of 2.8027(5) A in the d3 species is 0.0058(7) A shorter than the O-(H)⋯N distance found earlier for the d0 species (R. E. Penn and R. F. Curl, Jr., J. Chem. Phys.55, 651–658 (1971)). The anomalous rs structural parameters rOH = 1.14 A and ∠COH = 103.7°, when corrected for the systematic error caused by the O⋯N “shrinkage” upon deuteration, become 1.00 A and 108°, respectively.

The “syn-effect” in sulfines and carbonyl oxides: Conformational preferences of CH3CHSO and CH3CHOO☆☆☆

Abstract Theoretical calculations indicate that the preference of ethanethial S-oxide fop syn-stereochemistry with a staggered HCCH conformation, as determined by microwave spectroscopy, is explained in terms of orbital and eleotrostatic interactions between the terminal oxygen and methyl hydrogen atoms.

Microwave spectrum, centrifugal distortion, substitution structure, and dipole moment of sulfine, CH2SO

Abstract The microwave spectrum of the reactive species sulfine (CH 2 SO) has been studied. Assignments of 86 transitions of the ground vibrational state normal isotopic species, with J up to 60, have allowed a thorough centrifugal distortion analysis. With planarity implied by the I c - I a - I b value of 0.1333 amu A 2 , spectral assignments of seven other isotopic modifications have resulted in the following substitution bond lengths and angles: CH syn = 1.085 A, CH anti = 1.077 A, CS = 1.610 A, SO = 1.469 A, ⦠HCH = 121.86 ° , ⦠SCH syn = 122.51 ° , ⦠SCH anti = 115.63 ° , and ⦠CSO = 122.51 ° . From Stark effect measurements of the normal and d 2 species, the dipole moment has been determined to be 2.994 D, oriented 25.50° relative to the SO bond and 9.61° relative to the normal species “ a ” axis. At an initial pressure of 30 mTorr in a clean brass waveguide, the lifetime of sulfine at 25°C is ∼30 min.

Microwave spectrum of 2-propene-1-imine, CH2CHCHNH

Abstract The reactive species, 2-propene-1-imine, has been identified by its microwave spectrum as a pyrolysis product of diallylamine vapor (100 mTorr, 400°C). Two entirely planar forms are observed, both with an “ s-trans ” CCCN configuration. The lower energy rotamer has an “ anti ” CCNH configuration, with r CC = 1.453(3) A , r CC = 1.336(4) A , and ∠ CCC = 122.9(3)° and a dipole moment of 2.01(2) D with 1.13(1) D and 1.66(2) D “ a ” and “ b ” components. The higher energy rotamer has a “ syn ” CCNH configuration and a dipole moment of 2.51(2) D with 2.39(2) and 0.77(3) D the “ a ” and “ b ” components. From relative intensity measurements, the ground state energy difference is determined to be 0.9 ± 0.1 kcal mole −1 .

Microwave spectrum and hydrogen bonding in 2-dimethylaminoethanol

Abstract The microwave spectrum of the normal species of 2-dimethylaminoethanol gives rotational constants (MHz) A = 5814.0(2), B = 2214.54(2), and C = 2037.96(2) and a dipole moment of 2.56 D, with a, b, and c components (D) of 2.27(2), 0.3(1), and 1.16(5), respectively, consistent with a gauche OCCN configuration, and an OH⋯N type hydrogen bond, facilitated by a central CN configuration distorted approximately 23° from “staggered.” The hydroxy d1 species rotational constants (MHz) A = 5688.95(38), B = 2190.17(4), and C = 2028.00(4) are consistent with either the hydroxyl group structure r OH = 1.235 A and COH = 100.5° or a structurally normal hydroxyl group with an approximate 0.01 ArO⋯N shrinkage upon deuteration.

Hydrogen bonding and conformational equilibrium of 2-methylaminoethanol by microwave spectroscopy

Abstract From its microwave spectrum, 2-methylaminoethanol is found to exist in two rotameric forms, each having an intramolecular hydrogen bond of the type OH⋯N and a gauche OCCN configuration. The lower energy form ( GT ) has rotational constants (MHz) A = 12123.35 (31), B = 2653.774 (15), and C = 2400.756 (13), consistent with a CCNC configuration distorted ∼7° from the trans form. The dipole moment of the GT rotamer and its a , b , and c components are 2.756 (13), 2.272 (8), 1.336 (20), and 0.808 (18) D, respectively. The higher energy form ( GG ) has rotational constants (MHz) A = 8985.12 (31), B = 3076.388 (14), and C = 2868.664 (15), consistent with a CCNC configuration distorted ∼21° from the “staggered” gauche form (toward the trans form). The dipole moment of this rotamer and its a , b , and c components are 2.864 (11), 2.610 (11), 1.132 (11), and 0.331 (34) D, respectively. Relative intensity measurements give a ground state GG-GT energy difference of 0.46 (7) kcal mole −1 .

Microwave spectrum of cyclopropyl methyl sulfide

Abstract The microwave spectrum of cyclopropyl methyl sulfide gives rotational constants (MHz) A = 8777.38(9), B = 2681.43(2), and C = 2280.94(2), consistent with a gauche conformation, displaced from the C 8 cis form by 105.3° rotation about the cyclopropyl CS bond. From Stark effect measurements, the magnitude of the dipole moment is 1.495(8) D , with a , b , and c components of 0.1(1) D, 1.481(4) D, and 0.457(1) D, respectively. Ground state A - E splittings give a methyl barrier, V 3 , of 1913(40) cal/mole.

Microwave spectrum and hydrogen bonding in 1-aziridineethanol

Abstract From its microwave spectrum, 1-aziridineethanol, CH 2 CH 2 NCH 2 CH 2 OH is found to have a gauche OCCN configuration, maintained by an OH⋯N-type hydrogen bond. The normal species rotational constants (MHz), A = 8528.87(25), B = 2069.74(2), and C = 2020.41(2), are consistent with a small (∼6°) distortion from the “staggered” configuration about the central CN bond. Assuming a “normal” hydroxyl group, the hydroxy d 1 data suggest a decrease in the O⋯N distance upon bridge deuteration of ∼0.003 A. The dipole moment is 2.77(5) D, with 2.34(3), 1.45(6), and 0.3(3) D “ a ,” “ b ,” and “ c ” components, respectively.

THE PURSUIT AND CAPTURE OF SOME ELUSIVE ORGANOSULFUR MOLECULES

Abstract The use of flash vacuum pyrolysis-mass spectrometry, -microwave spectroscopy, and -photoelectron spectroscopy greatly facilitates the detailed study of such elusive molecules as sulfine (1), methanesulfenic acid (2), and cyclopropanethione valence tautomers (3). A brief description of the techniques used will be followed by a summary of some notable results achieved in our laboratories.