"Front Matter". In: Organosilanes in Radical Chemistry - Index of

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24 Thermochemistry calculated DH values for the silanes with the following substituents (in parentheses) are 383.3 (H) 387.8 (CH3), 384.4 (Cl), 394.5 (F), 379.3 (NH2), 388.5 (OH) and 376.1 (SH) kJ/mol. It is worth noting that the replacement of H by CH3 or OH increases the bond strength of ca 5 kJ/mol, whereas the replacement of H with NH2 or SH decreases the bond strength by 4 and 7 kJ/mol, respectively. 2.2.4 DERIVED BOND DISSOCIATION ENTHALPIES Due to the importance of homolytic bond dissociation enthalpies for understanding radical chemistry, a set of Me3Si w X bond dissociation enthalpies was derived via the relationship DH(Me3Si w X) ¼ DH f (Me3Si:) þ DH f (X:) DH f (Me3SiX) (2:10) Table 2.3 shows the DH f values for a variety of radicals and their corresponding Me3Si derivatives, together with the calculated like DH(Me3Si w X) from Equation (2.10). The DH(Me3Si w X) varies enormously through the series of compounds in Table 2.3 and strictly depends on the electronegativity of the X group. In general, the trends of DH(Me3Si w X) are the following. (i) For a particular column of the periodic table, the bond strength decreases going from top to bottom, i.e., X: DHf8(X:) a DHf8(Me3SiX) c,e H3C: 146:5 0:5 233:2 3:2 396 H3Si: 200:5 2 112:5 329 Me3Si: 16 6 b H2N: 188:7 1:5 291 f 496 Table 2.3 Derived Me3Si w X bond dissociation enthalpies (kJ/mol) 303:7 5:5 336 h Me2N: 145 c 248 4 409 HO: 39:3 0:2 500 3 555 MeO: 17:2 4 480 8 513 HS: 143:0 3 273 f 432 BuS: 59.5 d 381 3 457 F: 79:4 0:3 568 f 663 Cl: 121:3 0:1 354 3 491 Br: 111:9 0:1 298 4 426 I: 106:8 0:1 222 4 345 DH(Me3Si w X) g a From Reference [7], unless otherwise mentioned. b From Table 2.1. c From Reference [5]. d Calculated assuming DH(BuSwH) equal to DH((MeS H) ¼ 365:6kJ=mol [7]. e w Experimental data, unless otherwise mentioned. f Obtained from enthalpy/electronegativity correlation. g Rounded to the nearest 1 kJ/mol; Uncertainties 10 kJ=mol. h Direct measurement: 332 12 kJ=mol [6].
Ion Thermochemistry 25 Table 2.4 Recommended R w H bond dissociation enthalpies for some selected organic molecules (kJ/mol) a X w H DH(X w H) X w H DH(X w H) H3C H 439 0:5 H2NH 452:5 1:5 w w MeCH2 H 423 1:5 MeNH H 419 w w b Me2CH H 412:5 1:5 PhNH H 368 w w b Me3C H 404 1:5 HO H 499:15 0:20 w w CH2 w CH w H 465 3:5 MeO H 436 4 w C6H5 H 465 3:5 PhO H 371:3 2:3 w w c CH2 w CHCH2 w H 369 9 HS w H 381:5 3 PhCH2 w H 370 6 MeS w H 365:5 2 HC(O)CH2 w H 394:5 9 PhS w H 349:4 4:5 d N w CCH2 w H 396:5 9 H3Ge w H 349 8 HOCH2 w H 402 0:5 Bu3Ge w H 368 e HSCH2 w H 393 8 Ph3Ge w H 356 e MeC(O) w H 374 1:5 Bu3Sn w H 326 e a From Reference [7], unless otherwise mentioned. b The DH(Xw H) in MeNH þ 3 is 447 kJ/mol (i.e., 28 kJ/mol stronger) and in PhNHþ 3 (i.e., 60.5 kJ/mol weaker); see Reference [19]. c From Reference [20]. d From Reference [21]. e Data in solution [8]. is 307.5 kJ/mol Si w F > Si w Cl > Si w Br > Si w I, or Si w O > Si w S, or Si w C > Si w Si. (ii) For a particular row, the bond strength increases going from left to right, i.e., Si w C < Si w N < Si w O < Si w F, or Si w Si < Si w S < Si w Cl. In Table 2.4, we have collected background information for discussion in the following chapters. Recommended C w H bond dissociation enthalpies of selected organic compounds are reported in the first two columns, followed by a variety of heteroatom–hydrogen bond strengths including N w H, O w H, S w H, Ge w H, and Sn w H bonds. 2.3 ION THERMOCHEMISTRY Thermochemical information about neutral species can also be obtained from measurements of ions. Indeed, accurate bond dissociation energies for neutral molecules have been obtained from gas-phase ion chemistry techniques. In this section, we will summarize both the negative-ion and hydride-affinity cycles involving silicon hydrides (R3SiH) which are connected to electron affinity (EA) and ionization potential (IP) of silyl radicals, respectively [22–24]. 2.3.1 NEGATIVE-ION CYCLES Thermodynamic properties related to R3SiH can be obtained from negative-ion gas-phase studies. The following thermochemical cycle (cf. Scheme 2.1):
Page 1 and 2: Organosilanes in Radical Chemistry
Page 3 and 4: DEDICATION To my parents XrZstoB an
Page 5 and 6: viii Contents 3.6 Hydrogen Atom: An
Page 7 and 8: PREFACE A large number of papers de
Page 9 and 10: ACKNOWLEDGEMENTS I thank Keith U. I
Page 11 and 12: 2 Formation and Structures of Silyl
Page 19 and 20: 10 Formation and Structures of Sily
Page 27 and 28: 2 Thermochemistry 2.1 GENERAL CONSI
Page 29 and 30: Bond Dissociation Enthalpies 21 Tab
Page 31: Bond Dissociation Enthalpies 23 2.2
Page 35 and 36: Ion Thermochemistry 27 Table 2.5 El
Page 37 and 38: References 29 3. Goumri, A., Yuan,
Page 39 and 40: 32 Hydrogen Donor Abilities of Sili
Page 55 and 56: 4 Reducing Agents 4.1 GENERAL ASPEC
Page 57 and 58: General Aspects of Radical Chain Re
Page 59 and 60: Tris(trimethylsilyl)silane 53 Therm
Page 61 and 62: Tris(trimethylsilyl)silane 55 4.3.1
Page 63 and 64: Tris(trimethylsilyl)silane 57 A goo
Page 65 and 66: Tris(trimethylsilyl)silane 59 C(O)C
Page 67 and 68: Tris(trimethylsilyl)silane 61 radic
Page 69 and 70: Tris(trimethylsilyl)silane 63 86% y
Page 71 and 72: Tris(trimethylsilyl)silane 65 RO RO
Page 73 and 74: Tris(trimethylsilyl)silane 67 O AcO
Page 75 and 76: Tris(trimethylsilyl)silane 69 Tris(
Page 77 and 78: Other Silicon Hydrides 71 The reduc
Page 79 and 80: Other Silicon Hydrides 73 The decre
Page 81 and 82: Other Silicon Hydrides 75 Ph MeS O
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Other Silicon Hydrides 77 Table 4.6
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Silicon Hydride / Thiol Mixture 79
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Silylated Cyclohexadienes 81 and (4
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References 83 34. Kawashima, E., Uc
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References 85 104. Gimisis, T., Bal
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88 Addition to Unsaturated Bonds te
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90 Addition to Unsaturated Bonds ap
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92 Addition to Unsaturated Bonds 5.
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94 Addition to Unsaturated Bonds R
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96 Addition to Unsaturated Bonds Ph
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98 Addition to Unsaturated Bonds EP
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100 Addition to Unsaturated Bonds 5
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102 Addition to Unsaturated Bonds T
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104 Addition to Unsaturated Bonds R
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106 Addition to Unsaturated Bonds a
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110 Addition to Unsaturated Bonds S
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112 Addition to Unsaturated Bonds T
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114 Addition to Unsaturated Bonds I
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120 Unimolecular Reactions 1 Si(H)M
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122 Unimolecular Reactions t-Bu t-B
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124 Unimolecular Reactions MeO Si O
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126 Unimolecular Reactions t-Bu t-B
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128 Unimolecular Reactions R 1 R 2
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130 Unimolecular Reactions From the
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132 Unimolecular Reactions rearrang
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134 Unimolecular Reactions H 3 C +
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136 Unimolecular Reactions Br O Si(
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138 Unimolecular Reactions R3Si C C
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140 Unimolecular Reactions Me3Si O
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142 Unimolecular Reactions 43. Albe
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144 Consecutive Radical Reactions c
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146 Consecutive Radical Reactions O
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148 Consecutive Radical Reactions a
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150 Consecutive Radical Reactions d
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152 Consecutive Radical Reactions T
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154 Consecutive Radical Reactions M
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156 Consecutive Radical Reactions F
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162 Consecutive Radical Reactions i
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164 Consecutive Radical Reactions A
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168 Consecutive Radical Reactions r
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170 Consecutive Radical Reactions E
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174 Consecutive Radical Reactions A
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176 Consecutive Radical Reactions P
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178 Consecutive Radical Reactions f
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182 Consecutive Radical Reactions 1
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184 Consecutive Radical Reactions 8
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186 Silyl Radicals in Polymers and
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220 List of Abbreviations PED photo
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222 Index Carbonyl sulfide 111 Carb
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224 Index Organosilicon boranes 2,
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226 Index Triethylsilane as mediato
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