VIBRATIONAL ANALYSIS AND AB INITIO STUDIES OF PROPIOLIC ACID by EDMUND MOSES NSO NDIP, B.S., M.S. A DISSERTATION IN CHEMISTRY Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Approved August, 1987 ACKNOWLEDGEMENTS My educational experiences at Texas Tech University have been very rewarding and along the way, I have had the good fortune of being associated with a lot of people. Consequently, I am indebted to them and wish to express my sincere gratitude for their help. First of all, I wish to thank Professor R. L Redington, my research mentor, for his ever enduring support, guidance and patience throughout the course of my study. My special thanks also go to Professor R. E. Wilde, Jr. for his friendship throughout the years. To the members of my committee, I say thank you for your patience. My thanks also go to Dr. J. L Mills, Dr. R. D. Larsen, and Dr. Jim Liang and his associates at the University of Utah, Chemistry Department. I do recognize here the goodwill of Prof. Josef MichI of the University of Texas at Austin (formerly of the University of Utah). Financial support was received from Texas Tech University and the Robert Welch Foundation. I must thank the government and people of Cameroon for the scholarships given me throughout the many years of my education. To my kids, Edmund, Jr. and Laura, I say thanks for the smiles throughout the difficult moments that we all shared. I especially thank my wife, Grace Manyi Ndip, for the sacrifices she has made over the years and for her help in preparing parts of this dissertation. TABLE OF CONTENTS ACKNOWLEDGEMENTS ABSTRACT LIST OF TABLES LIST OF FIGURES LIST OF SCHEMES I INTRODUCTION TO THE STUDY OF PROPIOLIC ACID Literature Study and Review Propiolic Acid~An Attractive Model Scope of the Present Work II EXPERIMENTAL TECHNIQUES Matrix Isolation Technique Matrix Materials and Properties Chemicals Instrumentation Sample Preparation Sample Deposition III ASSIGNMENT TECHNIQUES IV THEORETICAL BACKGROUND TO MOLECULAR MECHANICS Introduction Fundamentals of the Molecular Mechanics of Propiolic Acid V VIBRATIONAL ASSIGNMENTS: INTERPRETATIONS AND DISCUSSION Introduction Vibrational Assignments and Interpretations Conclusions VI MATRIX EFFECTS Introduction Theories of Matrix Shifts Matrix Materials Crystal Data Matrix Enviromental Effects Results and Discussion Conclusions VII THEORETICAL BACKGROUND TO AB-INITIO CALCULATIONS FOR PROPIOLIC ACID Total Energy Evaluation Basis Sets Evaluation of the Total Molecular Energy Geometry Optimization Force Constant Evaluation and Vibrational Analysis Evaluation of One - Electron Properties Unimolecular Reactivities-Calculation of the Potential Energy Surface Electron Correlation and Configuration Interaction VIII MOLECULAR ORBITAL STUDIES OF PROPIOLIC ACID Computational Details iv Results Further Discussion Overall Conclusions from MO Studies IX OVERALL CONCLUSIONS REFERENCES APPENDICES A1. CALIBRATED VIBRATIONAL FREQUENCIES OF PROPIOLIC ACID (PA) A2. CALIBRATED VIBRATIONAL FREQUENCIES OF DIDEUTERATED PROPIOLIC ACID (PA-D2) A3. CALIBRATED VIBRATIONAL FREQUENCIES OF MONODEUTERATED PROPIOLIC ACID (PA-OD) B1. OBSERVED WATER FREQUENCIES (CM-"") ABSTRACT A vibrational analysis and ab initio studies of propiolic acid have been carried out in a two part study. In the first part, infrared matrix isolation spectra of propiolic acid isolated in solid argon, carbon monoxide, nitrogen and neon at 11-35K have been recorded in the range 4000 - 400 cm"^. Spectra were also recorded for the isotopically labeled O and H isotopomers isolated in argon and nitrogen matrices. Spectra have been interpreted using isotopic splitting patterns, correlations with spectra of related molecules, and MO normal coordinate analysis at the ab initio (6-31G* basis set) level and semi-emperical MINDO / 3 level using standard basis set. Computational studies using MINDO / 3 and GAUSSIAN 82 have been carried out to determine geometries, energies, dipole moments, rotational constants, vibrational frequencies, force constants, and one- electron properties. Comparisons have been made with experimental data to check the accuracy of computed molecular parameters. Various unimolecular decomposition channels have been investigated and possible bimolecular decomposition channels postulated. The computed structures and energies of various intermediates have been determined. The internal rotation (torsional) barrier for hydroxyl group relative to the C-0 bond has been determined at various levels and the conversion from the cis to trans conformer has been identified as a prerequisite for some decomposition channels. VI LIST OF TABLES 1.1 Rotational Constants and Centrifugal Distortion Constants (MHz) 1.2 Moments of Inertia and Hydrogen Atom Coordinates 1.3 Stark Effect Measurements 1.4 Spectroscopic Constants of Propiolic Acid 1.5 lETS Vibrational Data for Chemisorbed Propiolic Acid 1.6 Theoretical Total Energies 2.1 Selected Matrix Properties 2.2 Electrical Properties of Matrix Materials 2.3 Thermal Properties of Matrix Materials 2.4 Site Diameters of Matrix Materials 4.1 Cartesian Coordinates (3N) of Propiolic Acid 4.2 Internal Coordinates (R) 4.3 Internal Symmetry Coordinates for Propiolic Acid 5.1 Fundamentals of Normal Propiolic Acid Compared 5.2 Fundamental Frequencies of Deuteriopropiolic Acid (PA-D2) 5.3 The Fundamental Vibrational Modes of Propiolic Acid 5.4 S/^(HC=C) ^°'' Pi'op'Of^y' Chloride and Propionyl Fluoride 5-5 ^(P-C=C) ^ ^(H-C=C) Ratios for the H-C^C Deformation 5.6 Summary of Assignments for PA-D2 in the 680 - 400 cm-1 Region 5.7 Fundamental Frequencies of Matrix isolated Propiolic Acid Monomers in Argon vii 5.8 Fundamental Frequencies of Monomer Propiolic Acid Isolated in Nitrogen 129 5.9 Fundamentals of Monomer Propiolic Acids Isolated in Carbon Monoxide 130 5.10 Comparison of Observed and MINDO / 3 Calculated Frequencies 131 5.11 Comparison of Calculated versus Observed Frequencies for Ne / PA 132 6.1 Site Diameters 163 6.2 Oxygen-18 Congeners of HCCCOOH 6.3 "• ^O Congeners for Fundamentals of DCCCOOH 6.4 Frequencies for DCCCOOD Oxygen-18 Congeners 6.5 HCCCOOD Oxygen-18 Congeners 6.6 Matrix Shifts for the HCCCOOH Fundamentals in Various Matrices 6.7 Comparison of Matrix Isotope Effects between HCCCOOH and DCCCOOD (VHCCCOOH ' ^DCCCOOD) 6.8 Comparison of Matrix Isotope Effects between HCCCOOH and DCCCOOH (VHCCCOOH " ^DCCCOOH) 6.9 Comparison of Matrix Isotope Effects between DCCCOOH and DCCCOOD (VQCCCOOH " ^DCCCOOD) 6.10 Comparison of Matrix Isotope Effects between HCCCOOH and HCCCOOD (VHCCCOOH " ^HCCCOOD) 6.11 Comparison of Matrix Isotope Effects between HCCCOOD and DCCCOOD (VHCCCOOD " ^DCCCOOD) 7.1 One - Electron properties 8.1 Geometry of Cis Propiolic Acid, Structure (I) 8.2 Geometry ofTrans Propiolic Acid, Structure (II) 8.3 Dipole Moments of Cis Propiolic Acid, Structure (I) viii 8.4 Dipole Moments of Trans Propiolic Acid, Structure (II) 218 8.5 Rotational Parameters [(Calculated versus Experimental (GHz))] 219 8.6 Moments of Inertia 220 8.7 Cis / Trans Relative Stabilization Energies 221 8.8 Symmetry Coordinates of Propiolic Acid 226 8.9 Computed Diagonal Force Constants for Stnjcture (I) 227 8.10 Deviations in Calculated Diagonal Force Constants 228 8.11a Force Constants for Propiolic Acid (cis conformer - 8.11b 6-31G*) 229 8.11c Force Constants for Propiolic Acid (cis): 6-31G 230 8.12 Force Constants for Propiolic Acid (trans): 6-31G 231 4-31G Diagonal Force Constants for the Carboxyl 8.13 Group Modes Compared 234 Calculated Harmonic Frequencies (cm"^) for Cis Propiolic Acid, Structure (I) 235 8.14 Calculated Harmonic Frequencies (cm-1) for Trans Propiolic Acid, Stmcture (II) 236 8.15 Thermochemistry from Frequency Calculations for Cis Propiolic Acid, Structure (I) 239 8.16 Thermochemistry from Frequency Calculation for Trans Propiolic Acid, Structure (II) 240 8.17 Stabilization Energies and the Effects of Electron Correlation (kcal / mol.) 242 8.18 Total Atomic Charges for Propiolic Acid cis Propiolic Acid 243 8.19 ST0-3G Optimized Parameters for Cis PA Inversion to Trans PA 245 8.20 3-21G Optimized Parameters for Propiolic Acid Inversion Barrier 246 ix 8.21 6-31G* Optimized Parameters for Propiolic Acid Inversion Barrier 247 8.22 Molecular Parameters for Description of Intrinsic Reaction Coordinate 259 8.23 Molecular Parameters for Local Minima^nd Maxima on Reaction Coordinate (RC = Co - Hy) at the 6-31GSCF level 263 8.24a Calculated Harmonic Frequencies of (V) 267 8.24b Geometry, Energy, Dipole Moment of (V) at 6-31G level 268 8.25 Optimized Geometries and Corresponding Energies for HCCHCOO (T^) at 6-31G SCF level 275 8.26 Decomposition of trans - HCCHCOO (T-|) Complex, 4^2 277 8.27 Decomposition of cis - HCCHCOO (T-|) 284 8.28 Optimized Geometries and Energies for Decarbonylation Reaction Intermediate(VII) 290 8.29 Molecular Parameters for Stationary Points on Reaction Coordinate at the 6-31G SCF level 291 8.30 Harmonic Frequencies (cm"^) and Thermochemistry of the Metastable Reaction Intermediate (VII) 294 8.31 Comparison of Atomic Charges for Decarbonylation Intermediates at the 6-31G SCF level 295 LIST OF FIGURES 1.1 Microwave Model Structure of Propiolic Acid 7 2.1 Schematic Diagram of a Matrix Isolation Experiment 23 2.2 Sample Preparation Setup 30 2.3 ^®0-lsotope Exchange Reaction Vessel 32 2.4 Sample Deposition Setup 34 3.1 Effects of 50% '^ ^O-Enrichment in Oxygen Containing Molecule with Equivalent Oxygen Atoms 39 5.1 The Two Possible Structures of Propiolic