Stuart W. Staley

Microwave spectrum and molecular structure of vinyl isocyanide: experimental and theoretical evaluation of conjugation

Abstract Microwave spectra have been observed and analyzed for four monosubstituted isotopic forms of vinyl isocyanide. From the resulting rotational constants the heavy-atom structure is determined as follows: C1C2=1.338(4) A, C2N=1.379(6) A, NC3=1.174(6) A, ∠ C1C2N=122.5(7)°, ∠ C2NC3=178.2(12)°. The structural parameters are compared to the experimental values of several related molecules and to ab initio results at the HF/6-31G* and MP2/6-31G* levels. The experimental and theoretical results permit an evaluation of the relative conjugating ability of vinyl versus cyclopropyl and cyano versus isocyano.

Microwave spectrum, structure, and π conjugation of isocyanocyclopropane

The microwave spectrum of the normal isotopic species of isocyanocyclopropane and its three unique mono‐substituted 13C isotopic varieties have been investigated in their natural isotopic abundances. For the normal isotopic species, Stark modulation and RFMDR techniques lead to the following rotational constants: A=15 827.303±0.009 MHz, B=3734.004±0.002 MHz, and C=3515.892±0.002 MHz. These data, along with those for the three isotopic species, lead to the following heavy atom structural parameters: C1C2=1.521±0.007 A, C2C3=1.513±0.005 A, C1N=1.377±0.008 A, and C≡N=1.176±0.005 A. To within a precision of ±1°, the C–N≡C group is linear and is inclined at an angle of 123.4±0.6° to the plane of the ring. The structural parameters are compared to those of related molecules and interpreted in terms of a frontier molecular orbital model for the π conjugation of the cyclopropyl ring.

Synthesis of bridged dicyclooctatetraenes and alkynylcyclooctatetraenes by palladium-catalyzed coupling reactions

Abstract Bridged dicyclooctatetraenes have been synthesized by the palladium-catalyzed coupling of distannanes with bromocyclooctatetraene by employing the ligands tri(2-furyl)phosphine and triphenylarsine. The coupling of bromocyclooctatetraene with terminal alkynes is compared to couplings with alkynylstannanes for the preparation of alkynylcyclooctatetraenes.

Microwave spectrum, dipole moment, and a proposed structure for 1-cyanobicyclo[1.1.0]butane

The microwave spectra of the normal and the 2-13C isotopic species of 1-cyanobicyclo[1.1.0]butane have been observed and assigned, leading to the following rotational constants: (normal), A=8807.202 ± 0.004, B=2924.334 ± 0.002, C=2509.322 ± 0.002 and (isotope), A=8608.85 ± 0.85, B=2902.88 ± 0.02, and C=2478.56 ± 0.02 MHz. Measurements of the second-order Stark effect led toμT=4.08 ± 0.01 D. Based on the available microwave data coupled with geometryoptimizedab initio molecular orbital structures for cyanocyclopropane and 1-cyanobicyclo[1.1.0]-butane, a molecular structure for the latter molecule is proposed. Analysis of the dipole moments of these molecules and of bicyclo[1.1.0]butane has led to the conclusion that the bicyclobutyl group is a better electron donor than is cyclopropyl. In addition, a simple frontier molecular orbital model is not sufficient for explaining all of the structural changes that occur on substituting cyano at the bridgehead of bicyclo[1.1.0]butane.

Energetics of Bond Shift in Monohalogen-Substituted Cyclooctatetraenes

Abstract The free energies of activation for bond shift in fluoro-, chloro-, bromo- and iodocyclooctatetraene in THF- d 8 were determined by 13 C NMR spectroscopy to be 12.7, 15.0, 15.4 and 16.1 kcal/mol, respectively, at 298 K. Analysis of HF/6-31G*-optimized geometries and natural atomic charges for the ground state and ring inversion transition state for cyclooctatetraene (COT) and its monofluoro and monochloro derivatives indicates that the bond shift transition state for COT-F is stabilized (relative to COT) by electrostatic interactions between the fluorine and the flanking hydrogens, whereas those of the larger halogens are destabilized by steric interactions with the vicinal CH groups.

Crystal and Molecular Structures of (E)-(2-Phenylethenyl)cyclooctatetraene and (E)-(2-(4-Nitrophenyl)ethenyl)cyclooctatetraene. Conformations of Substituted Cyclooctatetraenes

The single crystal x-ray structures of (E)-(2-arylethenyl)cyclooctatetraenes 1 and 2 have been determined. The nitro group in 2 does not influence the geometry of the COT ring relative to that of 1. The influence of various substituents on several structural parameters of the COT ring are analyzed in terms of steric/electrostatic and electronegativity effects of the substituent.