5 | 7 | Computational Methods in Photochemistry

ABSTRACT

Simplest Nitrene, Imidogen Radical NH.................. 239 5.3 Photochemistry of Alkyl Azides and Properties of

Alkylnitrenes .............................................................. 243 5.3.1 Experimental Studies...................................... 243 5.3.2 Computational Studies.................................... 249

5.3.2.1 Methyl Azide and Methylnitrene...... 249 5.3.2.2 Calculations for Other Alkylnitrenes.. 257

5.4 Photolysis and Thermolysis of Vinyl Azides: Properties of Vinylnitrenes........................................ 262 5.4.1 Experimental Results...................................... 262 5.4.2 Computational Results on the Mechanism

of Azirine Formation and Properties of Vinylnitrene ..................................................... 265 5.4.2.1 Semiempirical and Early Ab Initio

Calculations........................................ 265 5.4.2.2 High-Level Ab Initio Calculations.... 266

5.5 Photolysis and Thermolysis of Acyl Azides: Properties of Acylnitrenes ......................................... 268 5.5.1 Early Experimental Results ........................... 268 5.5.2 Early Theoretical Results ............................... 275 5.5.3 Recent Computational and Experimental

Studies.............................................................. 278 5.6 Photolysis of Aryl Azides: Properties of

Arylnitrenes ................................................................ 282 5.6.1 Early Experimental and Theoretical

Studies.............................................................. 282 5.6.1.1 Experiments ....................................... 282 5.6.1.2 Semiempirical Calculations .............. 288

5.6.2 Phenylnitrene: Electronic Structure and Spectroscopy..................................................... 290 5.6.2.1 UV-Vis Spectroscopy of Triplet

Phenylnitrene .................................... 293 5.6.2.2 UV-Vis Spectroscopy of Singlet

Phenylnitrene .................................... 295 5.6.3 Dynamics of Singlet Phenylnitrene ............... 297

5.6.3.1 Recent Experiments........................... 297 5.6.3.2 Recent Ab Initio Calculations ........... 299

5.6.4 Spectroscopy of Substituted Phenylnitrenes................................................. 301

5.6.5 Substituent Effects on Intersystem Crossing............................................................ 306 5.6.5.1 Para-Substituted Derivatives of

Phenylnitrene..................................... 306 5.6.5.2 Ortho-and Meta Substituted

Derivatives of Phenylnitrene ............ 309 5.6.5.3 Calculations of the Spin-Orbit

Coupling.............................................. 310 5.6.6 Substituent Effects on the Rates and

Regiochemistry of the Ring Expansion of Phenylnitrene .................................................. 311 5.6.6.1 Inﬂuence of Para-Substituents: The

Electronic Effect................................. 315 5.6.6.2 The Inﬂuence of Ortho-Substituents:

Steric and Electronic Effects ............ 322 5.6.6.3 Ring Expension of Fluoro-Substituted

Singlet Phenylnitrenes ...................... 326 5.7 Conclusions ................................................................. 338 Acknowledgments................................................................ 340 References............................................................................ 340

5.1 INTRODUCTION

Compounds containing neutral, monovalent nitrogen atoms are known as nitrenes. The parent structure, NH, is called imidogen. Because most stable compounds of neutral nitrogen have a valence of three, it is no surprise that nitrenes are typically very reactive and short lived and, hence, are intermediates.