Reactive Intermediate Chemistry

1062 INDEX

Singlet-triplet energy gap (Continued) meta-benzynes, 750–752 naphthynes, 769

nitrenium ions

aryland heteroarylnitrenium ions, 608–611 hydrogen atom transfer, 630–631

parent, alkyland halonitrenium ions, 604–606

non-Kekule´ molecule

electron spin resonance (ESR), 168–170 limits of, 170–171

organic radical ions, intra-pair reactions, 241–246

phenylnitrene, computational chemistry, 525–528

ring expansion reactions, electronic structure calculations, 983–985

silylenes and germylenes, 661–662 electronic spectra, 664–665

singlet carbenes, 278–279

stable singlet carbenes, dimerization reactions, 347–350

tetramethylenebenzene (TMB), 185–187 tetramethyleneethane (TME), 183–185 trimethylene-methane (TMM), electron photodetachment photoelectron

spectroscopy, 177–179 triplet carbenes, 395–402

hydrogen abstraction, 404–405

laser flash photolysis (LFP), 412–413 preequilibrium mechanism, 395–400 solvent effects, 401–402

steric effects, 381–383 structural properties, 376–377

surface-crossing mechanism, 400–401 Singlet-triplet equilibration, singlet carbenes,

307–308

Singly-linked radical cations, bimolecular reactions, 249

Singly occupied molecular orbital (SOMO) organic radical ions

bifunctional/distonic radical ions, 231–234

p-donors, 215–218

protic, ionic, and polar solvents, 253–256

s donors, 220–221

strained ring cations, 223–228 structural analysis, 214–215 unimolecular reactions, 238–239

radical configuration, 122

radical stabilization energy and bond dissociation energy, 123–125

triplet carbenes, hyperconjugation effects, 381 Sirenin, carbene synthesis, diazo compounds,

574–575

Site effects, matrix isolation infrared spectroscopy, 831–832

ultraviolet-visible spectroscopy, 836–838 Size-consistent calculations, electron correlation,

configuration interaction (CI), 975 Skell hypothesis, singlet carbenes, stepwise vs.

concerted addition, 293–297 Skell-Woodworth rule, triplet carbenes, double

bond additions, 431–434

SN1. See Stepwise nucleophilic substitution SN2. See Bimolecular nucleophilic substitution

(SN2)

Sodium iodide, femtosecond time scale, 906–907

Sol-gel catalysis, N-heterocyclic carbenes (NHC), transition metal catalysis, 364–365

Solid-state laser systems, picosecond lasers, 876–878

Solvation, aliphatic nucleophilic substitution, tertiary carbons, nucleophilic solvation, 62–65

Solvent effects

aliphatic nucleophilic substitution, tertiary carbons, nucleophilic solvation, 62–65

carbocation photolysis, 20–21

carbon acidity-carbanion basicity, condensedphase measurements, 87–96

nucleophilic substitution, 1-phenylethyl derivatives (X-1-Y), 46–47

p bond homolysis/heterolysis, picosecond optical calorimetry, 893–894

protic solvents, carbocation lifetimes, 21–23 singlet carbenes, carbene mimics, 313–314 triplet carbenes

preequilibrium mechanism, 396 singlet-triplet energy gap, 401–402

Solvent separated radical ion pairs (SSRIP) heterolytic radical addition and fragmentation,

153–155

organic radical ions, 235–236 Solvolysis

aliphatic nucleophilic substitution, tertiary carbon, 59–65

carbocation reactivity, carcinogenesis, 33–34 carbocations

reactive intermediates, 4–5 reactivity mechanisms, 15–16 skeletal rearrangements, 8–9

Sonogashira coupling reactions, triplet polynuclear aromatic carbenes, 451–452

sp carbanions

carbon acidity-carbanion basicity condensed-phase measurements, DMSO

acidity, 88–90

hybridized C–H bonds, 86–87 geometry, 72

stable singlet carbenes, singlet vs. triplet ground state, 330–332

sp2 carbanions

carbon acidity-carbanion basicity, hybridized C–H bonds, 86–87

geometry, 72 sp3 carbanions

carbon acidity-carbanion basicity condensed-phase measurements, DMSO

acidity, 89–90

hybridized C–H bonds, 79–86 geometry, 71–72

stereochemistry and racemization, 72–74 ‘‘Special pair’’ chlorins, 206

‘‘Spectator substituents,’’ singlet carbenes, intramolecular reactions, 304–306

Spectrometers, matrix isolation apparatus, 811 Spectrophotometric measurements, carbon

acidity-carbanion basicity, 77 Spectroscopic analysis

nitrenium ions, 631–640

direct intermediate detection, 638–640 infrared/Raman spectra, 636–638 ultraviolet-visible spectra, 634–636

non-Kekule´ molecules, structural properties, 171

triplet carbenes, excited states, 435–437 Spectroscopic windows, matrix isolation

apparatus, 804–806 Spin allowed process

tetramethylpiperidine N-oxide, 430–431 triplet carbene oxygen reactions, 423

Spin conservation rules, tetramethylpiperidine N- oxide, 430–431

Spin delocalization substituent constant, halogen-protected diphenylcarbenes, 446–447

Spin density

organic radical ions, strained ring cations, 226–228

triplet carbene delocalization, 386–387 Spin equilibrium

laser flash photolysis, 429 non-Kekule´ molecules, ground-state

multiplicity, 174

Spin-forbidden process, triplet carbenes, matrix isolation studies, 425

INDEX 1063

Spin-induced deprotonation barrier, nitrenium ions, photochemical initiation, 616–618

Spin isomerism, non-Kekule´ molecules, 190–191 Spin multiplicity, organic radical ion, cation

reactive intermediates, 235–236 Spin-orbit coupling (SOC)

halogen-protected diphenylcarbenes, 445–447 phenylnitrene, intersystem crossing, 532

Spin restriction, triplet carbenes excited state spectroscopy, 438 laser flash photolysis, 428–429

Spin-spin interactions, triplet carbenes EPR spectroscopy, 385–386 isomerism, zero-field splitting, 388–389

Spin states

carbon atoms, 465

heterocyclic planar tetramethyleneethane (TME) derivatives, 190

long-lived (persistent) spin isomerism, 189–191 molecular connectivity, tetramethylenethane,

181–185 non-Kekule´ molecules

magnetic properties, 192 structural properties, 166, 170

singlet carbenes, stepwise vs. concerted addition, 291–297

statistical substate mixture, 194

triplet carbenes, hydrogen atom abstractions, 404

Spin statistical selection, radical structures, termination, 157

Spin trapping, radical identification/ characterization, 127

Split-valence basis set, LCAO-MO approximation, 971–973

Squalene synthase, carbocation reactivity, 34–35

Stabilization, azide ion at benzylic carbon, concerted reaction mechanism, 53

Stable germylenes

dialkylgermylene synthesis, 691–692 diarylgermylene synthesis, 692–694 kinetic stabilization reactions, 695–696

Stable ions

2-norbornyl cation, 11–12 persistent carbocations

chemical properties, 5–6 crystal structures, 13–15

isotopic perturbation of symmetry, 12–13 nonclassical ions, 9–12

rearrangement chemistry, 8–9 superacids, 5

theoretical background, 6–8

1064 INDEX

Stable plumbylenes, synthesis and reactions, 699–705

Stable radicals, structure and reactivity, 125–126 Stable silylenes, reactions and dimerizations,

684–691

dialkylsilylene synthesis and isolation, 684–687 overcrowded diarylsilylene generation and

reactions, 687–691

silylene-isonitrile complex reactions, masked silylene, 689–691

Stable singlet carbenes. See Carbenes Stable stannylenes, synthesis, structure and

reaction, 696–699 Stannylene-iron complex, 698–699 Stannylenes

diarylgermylkene synthesis, 694

synthesis, structures, and reactions, 696–699 Stannyl radicals, homolytic halogen/chalcogen

transfer, 147–148

‘‘Starburst’’ nondiazo compounds, triplet polynuclear aromatic carbenes, 450–452

Starredness, tetramethylene-ethane, 182 Stationary points, electronic structure calculations,

enthalpy predictions, 965–966 Statistical approximations, potential energy

surfaces (PES), 940–941 nonstatistical dynamics, effects, 955–956 reactive intermediate dynamics, 948–949

Statistical kinetic models, potential energy surfaces (PES), 937–943

phase space, 937–938

statistical approximation, 940–941 transition state hypothesis, 938–939 Steady-state approximations, radical chain reaction velocities, 136–138

Steepest descent calculations, potential energy surfaces (PES), transition states and bifurcations, 932–934

Stepwise addition 2-methylenecyclopentane,1,3-diyls, 180 organic radical ions, bimolecular reactions,

249–250

potential energy surfaces (PES), hypersurface typology, 926–931

singlet carbenes, concerted addition vs., 291–297

triplet carbenes

double bond additions, 431–434 hydrogen tunneling, 418–421

Stepwise nucleophilic substitution (SN1) aliphatic nucleophilic substitution, tertiary

carbons, 59–60

azide ion at benzylic carbon

benzyl derivatives, 58 concerted reactions coupling, 51–53 uncoupling, 56–57

ionization and trapping, liberated intermediates, 50

1-phenylethyl derivatives (X-1-Y), 46–47 preassociation reactions, 50–51 ring-substituted cumyl (X-2-Y) derivatives,

47–48

basic mechanisms and nomenclature, 41–43 radical nucleophilic substitution (SRN1),

heterolytic radical addition and fragmentation, 153

SN1 solvolysis, carbocation reactivity, 15–16 Stereochemistry (stereomutation)

carbanions, 72–74 1,1-difluorocyclopropane, 992–994 double bond additions, 431–434

ring opening stereochemistry, hyperconjugation reaction, 989–997

triplet carbenes, abstraction-recombination insertion, 404

Stereorandom reaction, 2- methylenecyclopentane,1,3-diyls, 180

Stereorigidity, organic radical ions, unimolecular reactions, 236–239

Stereoselective synthesis

stable singlet carbenes, transition metal catalysts, 363–365

unimolecular radical ion reactions, sigmatropic shifts, 236

Stereospecific addition silylene insertions

multiple bond additions, 677–680 single bond additions, 671

singlet carbenes, stepwise vs. concerted reactions, 291–297

Sterically bulky substituents, persistent triplet carbenes, 439–441

Steric effects dialkylgermylene, 691–692

diarylgermylene synthesis, 694

organic radical ions, protic, ionic, and polar solvents, 252–256

silylenes and germylenes, singlet and triplet states, 661–662

stable singlet carbenes, singlet vs. triplet ground state, 331–332

triplet carbenes, 379 dimesitylketone oxide, 425–426

singlet-triplet energy gap, 381–383 zero-field splitting, annealing, 390

tunneling reactions, elevated temperatures, 422 Steric protecting groups, persistent triplet

carbenes, 439–441

Steric strain, strained hydrocarbons, 726–727 Stern-Volmer equation, triplet carbenes

preequilibrium mechanism, 396 time-resolved ultraviolet-vis (TRUV-Vis), 394

Stilbenes

isomers, organic radical ions, intra-pair reactions, 242–246

picosecond lasers, 886–887

Stop-motion photography, femtosecond time scale, reaction dynamics, 901–902

Stopped-flow techniques, femtosecond time scale, 901–902

Strained alkenes, dimerization, 731–732 Strained hydrocarbon structures

angle deformation, 724–725

inverted tetrahedral geometries, 725–726 reactivity

cycloaddition reactions, 733 cyclopropanes, electrophilic cyclobutanes,

733–735

electronic spectra, 736 free radical reactions, 733 NMR spectra, 736

transition metal carbon-carbon bond cleavage, 735–736

vibrational spectra, 737 steric strain, 726–727 torsional strain, 726

twisted double bonds, 727–729 Strained ring cations, organic radical ions,

221–228 Strain energies

calculated energies, 719–721 calculational models, 721–724 experimental data, 718–719

Streak camera detection, picosecond systems, fluorescence spectroscopy, 880

Structural properties

femtosecond time scale, 919–920 singlet carbenes, 274–279

Styrene compounds

carbocation reactivity, nucleophilic additions, 27–28

carbon-alkene reactions, 474

germylene multiple bond addition, 679–680 Substituent effects

benzynes

meta-benzynes, 760–762 o-benzynes, 759–760 p-benzynes, 762–764

INDEX 1065

cubyl cation formation, 986–987

ring expansion reactions, electronic structure calculations, 983–985

Substituted benzenes, carbon atom reactivity with Substituted phenylcarbenes, triplet carbenes,

electronic effects, 379–380 Substitution, homolytic, bimolecular (SH2)

reaction, hydrogen atom transfers, 145–146

Sulfides, single bond silylene insertions, 669–671 Sulfones, carbanion stereochemistry and

racemization, 74 Sulfonylnitrenes, 517–518

Sulfur atoms, organic radical ions, n donors, 218 Superacid media

biosynthesis, 35 carcinogenesis, 33–34 nitrenium ion studies, 631–632 nonclassical structures, 11–12 persistent carbocations, 5 X-ray crystallography, 14–15 zeolite carbocations, 32–33

Superconducting quantum interference devices (SQUID), non-Kekule´ molecules, magnetic properties, 191–192

Super electrophilic carbenes, singlet carbenes, philicity addition, 283–285

Superposition of states, femtosecond laser pulses sodium iodide, 907

uncertainty principle, 905–906 Surface-crossing mechanism, triplet carbenes,

singlet-triplet energy gap, 400–401 Symmetric spectra

isotopic perturbation, 12–13 trimethylenemethane (TMM), 175

Symmetry parameters

potential energy surfaces (PES), reactive intermediate dynamics, 949–950

singlet carbenes, transition state, 289–291 Synthesis

carbenes

diazo compound catalysis, 572–579 cyclopropanation/cyclpropenation,

573–575

diazocarbonyl compounds, 578–579 electrophilic/nucleophilic compounds,

563

insertion reactions, 575–577 ylide formation, 578

electrophilic/nucleophilic metal compounds, 563

alkylidenes, 570–571

diazo compound catalysis, 565–567

1066 INDEX

Synthesis (Continued) metathesis, 469–570

transition metal complexes, 567–569 Fischer carbene complexes, 579–580 ring-closing metathesis, 581–582 structural properties, 561–563

nitrenes, metal compounds, organic synthesis, 583–586

Schlenk-Brauns hydrocarbons, 167

Taft-type correlation, singlet carbenes, intermolecular insertions, 302

Tamoxifen, carbocation reactivity, 33–34 Tbt-substituted diarylgermylene, 693–694 Tbt(Tip)GeBr2, 692–694

Tebbe reagent, carbene synthesis, alkylidines, 570–572

Temperature dependence

hydrogen atom transfer kinetics, 417 triplet carbenes

electron paramagnetic resonance spectroscopy, 386–390

hydrogen tunneling reactions, 421–422 time-resolved spectroscopy, room

temperature solution, 392–394 Temperature-jump techniques, femtosecond time

scale, 901–902

Termination rate constant, radical structures, 157

Termination reactions, radical structures chain reaction sequence, 134–135 closed-shell compounds, 156–157

Tertiary amines

radical cations, intra-pair reactions, 243–246

single bond silylene insertions, 669–671 Tertiary carbon, aliphatic nucleophilic substitution

reaction mechanism, 59–62 solvent/solvation, 62–65

Tetraacetate, acylnitrenes, 511 Tetraalkyldisilene, 689

Tetracene, organic radical ions, p-donors, 215–218

Tetrafluoro-4-oxocyclohexa-2,5-dienylidene, hydrogen tunneling, 418–421

Tetrahedrane, 731 Tetrahydrofuran (THF)

carbon acidity-carbanion basicity, condensedphase measurements, ion-pair acidities, 90–93

carbon atom deoxygenation, 487–488 femtosecond time scale, oxyalkyl diradical/

formylalkyl radical intermediates, 917

Tetrahydropyran, femtosecond time scale, oxyalkyl diradical/formylalkyl radical intermediates, 917

Tetrakis(aryl)ethylene, persistent triplet carbenes, 440–441

2,3,5,6-Tetrakis(methylene)-1,4-cyclohexanediyl, disjoint properties, 185–186

Tetramethyl-2-indanone, silylene multiple bond additions, 681–683

1,2,4,5-Tetramethylbenzenene, CASPT2 calculations, 977

1,1,3,3-Tetramethylbutatriene, silylene multiple bond addition, 678–680

Tetramethylenebenzene (TMB) oxygen reactions, 185 singlet-triplet separation, 185–187

Tetramethylene diradicals, femtosecond time scale, 915–916

Tetramethyleneethane (TME)

heterocyclic planar derivatives, 188–191 non-Kekule´ molecule

electron spin resonance (ESR), 170 Hund’s rule, 167–168

singlet-triplet separation, 183–185 spin-state dependent molecular connectivity,

181–185

Tetramethyloxirane, radical cation, 231 2,2,6,6-Tetramethylpiperidine N-oxide (TEMPO)

stability and persistence, 125–126 triplet carbenes, oxygen reactions,

430–431

Tetramethylsilirene, silylene multiple bond addition, 675–677

1,1,2,2-Tetraphenylethene (TPE), picosecond spectroscopy, p bond homolysis/ heterolysis, 892–894

Tetraradical structures, m-quinonoid non-Kekule´ molecules, 187–188

Tetrathiaplumbolanes, 701–705

Thermal deazetiziation, potential energy surfaces (PES), 2,3-diazabicyclo[2.2.1]hept-2-ene, 953–955

Thermal dissociation, overcrowded diarylsilylenes, 687–689

Thermalization, matrix isolation, 802 Thermal reactivity, small ring hydrocarbons,

730–731

Thermal retrocycloaddition, diarylgermylene synthesis, 692–694

Thermodynamically favored configuration, triplet carbenes, excited state spectroscopy, 438

Thermodynamic control diarylgermylkene synthesis, 694

organic radical ions, protic, ionic, and polar solvents, 251–256

overcrowded diarylsilylenes, 687–689 persistent triplet carbenes, 439–441

Thermolysis cyclotrisilanes/cyclotrigermanes, 656–657 polysilanes and oligosilanes, 652–654 radical chain reaction sequence, velocity

measurements, 137–138

radical initiation, closed-shell compounds, 140–142

singlet carbenes, philicity addition, 283–285 Thiagermirane, 695–696

germylene multiple bond additions, 683 Thiasilarane, silylene multiple bond additions,

681–683

1,3-Thiazol-2-ylidenes, stable singlet carbenes, p- electron-donating heteroatom substituents (D-C-D), 339–340

Thienamycin, carbene synthesis, 579 Thiocarbonyl compounds, silylene/germylene

multiple bond additions, 680–683 Thioketones, silylene multiple bond additions, 683 Thiones, group transfer reactions, 156 Thiophenes, carbon atom reactivity, 485 Threefold coupling, triplet polynuclear aromatic

carbenes, 448–449

Threonine, carbon atom reactions, 472 Through-bond interaction

p-benzynes

parent structure, 758–759 substituent effects, 763–764

future research, 785 hetarynes, 778–782 naphthynes, 767–769

Through-space interaction, halogen-protected diphenylcarbenes, 446–447

Time-correlated single-photon counting(TCSPC), picosecond systems, 880–881

Time-delayed pulse, femtosecond time scale, structural determinations, 919–920

Time-dependent density functional theory (TD)DFT

matrix isolation, 838

wave function vs. DFT calculations, 981 Time-resolved absorption spectroscopy

meta-benzynes, 751–752

nanosecond laser flash photolysis, 849–868 data acquisition and processing, 851–852 decay kinetics analysis, 869

flow systems, 869 future applications, 868 kinetic studies, 853–854

INDEX 1067

probe technique, 858–864

quantum yields and extinction coefficients, 865–868

second-order processes, 864–865

radical identification/characterization, 133–134 radical ion detection-observation, 212–214

Time-resolved electron paramagnetic resonance, triplet carbenes, excited states, 437–438

Time-resolved femtosecond dynamics, basic principles, 903–904

Time-resolved infrared spectroscopy (TRIR) nitrenium ions, 636–638

singlet-triplet equilibrations, 307–308 triplet carbenes, 394

surface-crossing mechanism, 400–401 Time-resolved laser flash ESR spectroscopy

organic radical ion detection-identification, 213 triplet carbenes, oxygen reactions, 423–425

Time-resolved resonance Raman (TRRR) spectroscopy, nitrenium ions, 636–638

Time-resolved spectroscopy, triplet carbenes, room temperature solution, 392–394

infrared (TRIR) spectroscopy, 394 ultraviolet-vis (TRUV-Vis) spectroscopy,

393–394

Time-resolved ultraviolet-vis (TRUV-Vis) spectroscopy, triplet carbenes

room temperature solutions, 393–394 singlet-triplet energy gap, surface-crossing

mechanism, 400–401

119Sn NMR, stannylene structures, 697–699 Tin hydride reaction

nonchain radical reaction sequence, 138–140 radical chain reaction sequence, 134

Tin-tin bonds, overcrowded diarylsilylenes, 687–689

Tolualdehydes, carbon atom deoxygenation, 489–492

carbene formation, 489–490

Toluene, carbon atom reactivity, benzene/ substituted benzene, 480–484

Tolylcarbenes, carbon atom deoxygenation, 489–492

p-Tolylcarbene, phenylcarbene rearrangement, incarcerated carbene chemistry, 316–317

Tolylnitrene, azirine cyclization, 535–536 o-Tolylcarbene, carbon atom reactivity, 480–484 Toplogical requirement, triplet polynuclear

aromatic carbenes, 451–452 Torsional strain, strained hydrocarbons, 726 Tosylazide, 517–518

Tosylnitrene, electron paramagnetic resonance (EPR) spectroscopy, 517–518

1068 INDEX

N-Tosyl-3,4-dimethylenepyrrole, long-lived (persistent) spin isomerism, 189–191

Trans-1,2-dichlorfoethylene, single bond insertions, 671

Trans-cyclooctene, twisted double bonds, 727–729 Trans-HNNO, matrix isolation spectroscopy, 507 Transient radicals, mechanistic probe, 126–127 Transient singlet carbenes, stable singlet carbene

comparisons, 365–366 Transient spectroscopy

nanosecond laser flash photolysis, 852–853 picosecond lasers, 877–878

Transition metal complexes carbene synthesis, 567–569

carbon-carbon bond cleavage, 735–736 germylene synthesis, 696

spin isomerism, 191

stable singlet carbenes, catalytic applications, 358–365

electronic structures, 359–362 Transition state theory (TST)

carbocation reactivity, rate-equilibrium correlation, 23–25

cyclopropane stereochemistry, 991–997 electronic structure calculations, enthalpy

predictions, 965–966 femtosecond time scale, 902, 922

nucleophilic substitution at benzylic carbon coupling stabiliization, 53

cumyl (X-2-Y) coupling stabilization, 55–56 potential energy surfaces (PES)

bifurcations, 931–934 limitations, 956–957

statistical kinetic models, 938–939, 942–943 stepwise vs. concerted reaction mechanisms,

929–931 singlet carbenes

addition symmetry, 289–291 carbon–hydrogen insertions, 298–302 cycloadditions, 433

intramolecular reactions, 303–306 philicity, 280–285

triplet carbenes, hydrogen abstraction, product studies, 405

Transoid,transoid conformation 1,1-difluorocyclopropane, 993–994 1,2-dimethylspiropentanes stereomutation, 996 1,1-disilylcyclopropane stereomutation

calculations, 994–995 Trans-Stilbene radical anion

intra-pair reactions, 242–246 picosecond lasers, 886–887

Trapping agents, radical identification, 126–127

Trapping reactions, matrix isolation, 829–830 Triangular transition state, triplet carbenes,

hydrogen abstraction, 405 Triangulene

non-Kekule´ molecule, Hund’s rule, 167–168 oxygen trianion biradicals, 197

1,2,4-Triazol-5-ylidene, stable singlet carbenes cyclopropanation, 351–354 p-electron-donating heteroatom substituents

(D-C-D), 339–340

Tricyclane radical cations, bimolecular reactions, 252

Tridehydrobenzene, hetarynes, 778–782 Tridehydrobenzyne, 782 2,2,2-Trifluoroethanol (TFE)

carbocation lifetimes, 21–23 photoprotonation, 19–21

2-Trifluoromethyldiphenylcarbene, tunneling reactions, elevated temperatures, 422 Trifluoromethyl azide, alkylnitrenes, 510–511

Trifluoromethyl groups diphenylcarbene protection, 447–448 triplet diphenylcarbenes, 447–448

Trifluoromethyl substituents, stable singlet carbenes, single electronically active heteroatomic substituents, 343–347

Trigonal-pyramidal geometry, carbanions, 71–72 2,4,6-Triisopropylphenyl group (Tip group),

692–694 Trimethylene

diradicals, femtosecond time scale, 901–902, 915–916

oxyalkyl diradical/formylalkyl radical intermediates, 917

extended Hu¨ckel (EH) calculations, 989 Trimethylene-methane (TMM)

bifunctional/distonic radical ions, 229 bimolecular trapping, 176–177 electron photodetachment photoelectron

spectroscopy, singlet-triplet gap, 177–179 electron spin resonance (ESR), 168–170

spectral characteristics, 174–175 Hund’s rule, 167–168

matrix isolation, 820

radical cation, intra-pair reactions, 242–246 ring closure chemistry, 175–176 ring-constrained derivatives, 2-

methylenecyclopentane,1,3-diyls, 179–181

2,3,4-Trimethylenepentane-1,5-diyl, non-Kekule´ structure, disjoint vs. parity-based predictions, 192–194

Trimethylimine, alkylnitrenes, 508–511

(2,4,6-Trimethylphenyl)carbene, preequilibrium mechanism, 396

2,4,6-Trimethylphenylnitrene azirine cyclization, 535–536 intersystem crossing, 534

Triphenylmethyl cation basic properties, 4

X-ray crystallography, 13 Triphenylmethyl radical, stability, 125–126 Triphenylphosphine telluride, 695–696 Triplet 1,3-diradical, double bond additions,

431–434

Triplet back electron transfer (BET), intra-pair reactions, 239

Triplet biradicals, intra-pair reaction, 245–246 Triplet ground state

alkenes, Diels-Alder reactions, 180 alkylnitrenes, 510–511

p-benzynes, substituent effects, 762–764 carbenes

basic properties, 376–377 direct observation, 384

double bond additions, 431–434 electronic effects, 378–380 excited states, 434–439

geometry, 437–438 product studies, 434–435

reactivity differences, 438–439 spectroscopic studies, 435–437 generation and reaction, 383–384

hydrogen atom abstraction, 402–422 chemically induced dynamic nuclear

polarization, 406–408 laser flash potolysis, 408–413 product studies, 402–405 tunneling reactions, 413–422

atomic transfer kinetics, 416–417 intramolecular reactions, 419–421 pathway determination, 417–419 product studies, 413–416 temperature elevations, 421–422

hyperconjugation effects, 380–381 maxtrix-isolated spectroscopy, 385–392

electron spin resonance (ESR), 385–390 fluorescence, 391

infrared spectroscopy, 391–392 ultraviolet-visible spectroscopy,

390–391

oxygen reactions, 422–431 dimesitylketone oxide, 425–426 emission, 426–427

laser flash photolysis, 427–429

matrix isolation spectroscopy, 423–425

INDEX 1069

product studies, 423 tetramethylpiperidine N oxide (TEMPO),

430–431

persistent triplet carbenes, 439–452 alkyl-protected diphenylcarbenes,

441–444

halogen-protected diphenylcarbenes, 444–447

high-spin polycarbenes, 449–452 polynuclear aromatic carbenes, 448–449 trifluoromethyl-protected

diphenylcarbenes, 447–448 singlet carbenes

singlet-triplet equilibration, 307–308 stepwise vs. concerted addition, 293–297 structural comparisons, 377–378

singlet-triplet equilibration, 307–308 singlet-triplet gap estimation, 395–402

preequilibrium mechanism, 395–400 solvent effects, 401–402 surface-crossing mechanism, 400–401

stable singlet carbenes, singlet vs. triplet ground state, 330–332

steric effects, 379, 381–383 time-resolved spectroscopy, room

temperature solution, 392–394 infrared (TRIR) spectroscopy, 394

ultraviolet-vis (TRUV-Vis) spectroscopy, 393–394

carbon atoms, inorganic substrates, 471 didehydrotoluene biradical, 771–773 diphenylcarbenes, rates and activation

parameters, 285–289 imidogen, 503–506

matrix isolation spectroscopy, 507 long-lived (persistent) spin isomerism, 189–191 methylene, 274–276

methylnitrene, 509–511 nitrenium ions

aryland heteroarylnitrenium ions, 607–611 historical background, 602–603

hydrogen atom transfer, 629–631

parent, alkyland halonitrenium ions, 603– 606

photochemical initiation, 615–618 non-Kekule´ molecules

biradical vs. radical pair structure, 173 Curie law, ground-state multiplicity, 174 ESR zero-field splitting, 172–173

spin state preference, 170

organic radical ions, intra-pair reactions, 240– 246

phenylnitrene, 524–525

1070 INDEX

Triplet ground state (Continued) azirine cyclization, 534–536 computational chemistry, 526–528 singlet dynamics, 530–531

phosphinidines, 547–551

silylenes and germylenes, 660–662 tetramethylenebenzene (TMB), 186–187 tetramethyleneethane (TME), 183–185 trimethylene-methane (TMM)

ring closure chemistry, 176 ring-constrained derivatives, 180–181

vinylnitrenes, 520–522

Triplet sensitization, acylnitrenes/ carbonylnitrenes, 513–515

Triplet-triplet fluorescence, triplet carbene excited state, 434

2,4,6-Tris[bis(trimethylsilyl)methyl]phenyl, 687–689

[2,4,6-Tris(tert-butylphenyl)](phenyl)- diazomethane, triplet diphenylcarbene protection, 441–444

Tris(carbene), triplet polynuclear aromatic carbenes, 452

Trisilanes, photolysis, 655–656 [2,4,6-Tris(trifluoromethyl)phenyl]stannylene,

697–699

2,4,6-Tri-tert-butylphenyl groups, 698–699 Trityl radical

halogen-protected diphenylcarbenes, 447 stability and reactivity, 125–126

triplet carbenes, halogen-protected diphenylcarbenes, 447

Trivalent carbon compounds, organic radical ion chemistry, 207–209

Trolley systems, matrix isolation apparatus, 810 Tropone, benzene-carbon atom reactivity,

481–484

Tropylium fluoroborate, carbon atom reactivity with, 478

Tropylium ion, structural studies, 4

T-T fluorescence, triplet carbenes, excited state geometry, 438–439

Tunneling reactions, triplet carbenes, hydrogen atom tunneling, 413–422

atomic transfer kinetics, 416–417 intramolecular reactions, 419–421 pathway determination, 417–419 product studies, 413–416 temperature elevations, 421–422

Turbomolecular pumps, matrix isolation apparatus, 809–810

Twisted double bonds, strained hydrocarbons, 727–729

Two-bond pluck mechanism, singlet carbenes, stepwise addition vs. concerted reaction, 295–297

Two-dimensional electron spin transient nutation (2D-ESTN) spectroscopy

high-spin polycarbenes, 452

triplet polynuclear aromatic carbenes, 452 Two-electron amine oxidation, nitrenium ions,

602–603

Two-electron operators, Hartree-Fock calculations, 969–970

Two-parameter equations, carbocation reactivity, rate-equilibrium correlation, 24–25

Two-photon process, nanosecond laser flash photolysis, 869

Ultrafast electron diffraction, femtosecond time scale, structural determinations, 919–920

Ultrafast laser excitation, femtosecond laser pulses, coherence mechanism, 905–906

Ultrasound activation

metal-induced a-elimination reactions, 658–660

silylene multiple bond addition, 675–677 Ultraviolet (UV) spectroscopy

dimethylsilylene generation, 654–655

singlet carbenes, absolute rates and activation parameters, 285–289

Ultraviolet-visible (UV-vis) spectroscopy absorption spectroscopy, picosecond lasers

dye lasers, 878–880

solid-state laser systems, 876–878 electronic structure calculations, 964

CASPT2 methods, 977 matrix isolation, 836–838 nitrenium ions, 634–636 non-Kekule´ molecules, 194–195

structural properties, 171

organic radical ions, detection-observation, 212–214

phenylnitrene, 526–528 picosecond lasers, 875–880

radical identification/characterization, 133–134

singlet-triplet equilibrations, 307–308 tetramethylenebenzene (TMB), 186–187 triplet carbenes, matrix isolation, 390–391

Uncertainty principle, femtosecond time-resolved experiments, coherence mechanisms, 904–906

Uncoupled concerted reactions, azide ion at benzylic carbon, cumyl derivatives (X-2-Y), 56–57

Unimolecular radical ion reactions cationic intermediates, 236–239

picosecond laser spectroscopy, diphenylethene (stilbene), 886–887

Unpaired electron spins

non-Kekule´ molecules, ESR zero-field splitting, 173

radical compound identification

electron nuclear double resonance (ENDOR) spectroscopy, 131–132

electron spin resonance (ESR), 130–131 triplet carbenes, excited state geometry, 439

‘‘Unperturbed’’ test molecule, non-Kekule´ molecules, 195

a,b-Unsaturated ketone, radical anions, intra-pair reactions, 243–246

Unstarredness, tetramethyleenethane, 182

Vaccuum equipment, matrix isolation apparatus, 809–810

Vaccuum shroud, matrix isolation apparatus, 803–804

Vaccuum ultraviolet spectra, strained hydrocarbons, 736

Valence bond theory, tetramethyleneethane molecules, 182–183

Valence-shell electron-pair repulsion (VSEPR) theory

imidogen configuration, 504–506 singlet carbenes, structure and bonding,

276–279

Valence triple zeta basis set, electronic structure calculation, 972–973

Valley-ridge inflection (VRI) point, potential energy surfaces (PES), transition states and bifurcations, 932–934

van der Wals radii, halogen-protected diphenylcarbenes, 445–447

Variationally correct LCAO/MO, electronic structure calculation, 971–973

Variational transition state theory (VTST), potential energy surfaces (PES), 943

Velocity measurements, radical chain reactions, 136–138

Vertical radical cation, distonic structures, 230

Vibrational spectra

electronic structure calculations, enthalpy predictions, 966

femtosecond time scale, 1,3-dibromopropane, 910

strained hydrocarbons, 737 2-Vinylsiliranes, 689–691

INDEX 1071

Vinylacetylene, carbon atom reactions, 476–477

Vinylcarbenes

carbon-alkene reactions, 474 carbon atom reactions, 476–477 phosphinidines, 548

Vinyl chlorides, singlet carbenes, intramolecular insertion reactions, 304–306

Vinylchlorogermanes, single bond insertions, 671

Vinylcyclopropane rearrangement

organic radical ions, strained ring cations, 222–228

potential energy surfaces (PES) reactive intermediate dynamics, 950

stepwise vs. concerted reaction, 927–931 Vinyldiazoacetates, carbene synthesis

diazo compound synthesis, 573 insertion reactions, 576–577

Vinylidenes benzadiynes, 783–784 cyclo[6]-carbon, 784

meta-benzynes, 751–752 nitrenium ion classification, 596

Vinyl imines, germylene multiple bond additions, 683

Vinyl ketones, germylene multiple bond additions, 683

Vinylnitrenes

future research, 552

phenylnitrene computational chemistry, 525–528

phosphinidines, 548–551

structural characterization, 520–522 Vinylphosphinidine, structural properties,

548–551

Vinylphosphirane, flash vacuum pyrolysis, 548 Vinyl radicals

electron spin resonance (ESR), 131 structure, 123

Virtual orbitals, electron correlation, 973–974 Volumes of activation, singlet carbenes, 289

Walsh orbitals, organic radical ions, strained ring cations, 225–228

Wanzlick equilibrium, stable singlet carbenes, 334–335

Water

carbon atom reactivity, carbohydrate formation and, 472–473

nitrenium ion singlet-state reactions n nucleophile additions, 621–624 ultraviolet-vis spectra, 635–636