Presentation is loading. Please wait.

Presentation is loading. Please wait.

Organic photochemistry and pericyclic reactions (CY50003) 3-0-0.

Similar presentations


Presentation on theme: "Organic photochemistry and pericyclic reactions (CY50003) 3-0-0."— Presentation transcript:

1 Organic photochemistry and pericyclic reactions (CY50003) 3-0-0

2 Course content Principles of photochemical reactions; Excited states and their properties; experimental set up for photochemical reactions(1); Several useful photochemical reactions and their applications in organic synthesis (isomerization, Patterno-Buchi reaction (1), Norrish type I and II reaction(1), Photoreduction, Rearrangements: di-π- methane, oxa di-π- and aza di-π-methane rearrangements(2), Photocycloaddition (2), Photochemical aromatic substitution reaction (1), Reactions with singlet oxygen (1), Photochemical methods for protection and deprotection(2). Photochemistry of biological systems (photosensitized reactions of DNA/RNA, DNA damage and repair-1).

3 Books CRC Handbook of Photochemistry and Photobiology. Eds by. William M. Horspool and Pill-Soon Song CRC Press. ISBN: Synthetic organic photochemistry. Eds by. William M. Horspool, Plenum press ISBN: X

4

5

6

7

8

9 LIGHT ABSORPTION AND FATE OF EXCITATION ENERGY: Franck-Condon Principle Ground state (E0) and two excited states (E1, E2) of a molecule (vibrational and rotational levels are not shown).

10

11

12

13

14

15

16

17

18

19

20

21 Criteria of an ideal sensitizer It must be excited by the irradiation to be used, small singlet triplet splitting. High ISC yield. It must be present in sufficient concentration to absorb more strongly than the other reactants under the condition. It must be able to transfer energy to the desired reactant, low chemical reactivity in Triplet state.

22 Experimental set up for photochemical reactions Synthetic organic chemist (high intensity light source, easy to handle, various Flask size, specially designed systems) Physical chemist or physical-organic Chemist (mechanistic study)

23

24

25 Wavelength of cutoff (nm)Chemical composition Below 250Na 2 WO 4 Below 305SnCl 2 in HCl (0.1 M) Below 3302M Na 3 VO 4 Below 355BiCl 3 in HCl Below 400KH phthalate + KNO 2 (in glycol at pH = 11) Below M K2CrO 4 (NH 4 OH-NH 4 Cl at pH = 10) Above 3601 M NiSO 4 + 1M CuSO 4 (in 5% H 2 SO 4 ) Above 450CoSO 4 + CuSO 4 Short and Long cutoff filter solutions

26 Immersion Well Reactors Components # Lamps # Immersion wells # Reaction flasks # Standard flasks # Gas inlet flasks # Flow-through flasks # Larger capacity standard flasks

27 Non-Rotating Annular Photochemical Reactor # Large Quartz immersion well. # 400 watt medium pressure mercury lamp. # Reactor base and carousel assembly (non rotating), including support rod and immersion well adjustable clamp. # set of sample tube support rings for eight 25mm sample tubes # Only the inner or the outer tubes may be irradiated effectively at one time # UV Screen:- consisting of three black coated consisting of three black coated aluminum sections. A light tight lid, a removable front and back section, that are joined by means of a light tight seal

28 Semi-Micro Reactor The semi-micro is a low cost, easy-to-use device for irradiating a standard 1 cm cuvette (or small tube) with either 254nm or 350nm radiation for any preset time between 1 and 70 minutes. This reactor is ideal for preliminary studies of small volumes of solution.

29 # The multilamp reactors consist of a base, lid, six or three lamp modules. Each module contains two lamps. # The base is hexagonal and provided with a centrally located fan # A number of modules up to six or three may be operated. # Switches are provided to control the fan and lamp modules. # Supports from the lid hold samples inside the reactors. Magnetic strips are used to eliminate light leaks between the lamp modules. Multilamp Reactors: Six and Three Modules

30 Complete photochemical reactor comprising: * Multilamp reactor base with cooling fan and control switches * Three twin lamp modules * Six lamps of customers choice * Magnetic light sealing strips One set of attachments for supporting the reaction flask comprising : * Reaction flask support base * Flask support rod holder * Support rod hinged lid

31 Purity of solvent and gases Dilution (suppression of side reaction e.g., polymerization and dimerization.) Spectral transmission of solvent ( solvents devoid of low-lying excited states are best) Purity of solvent (Oxygen free, impurities free)

32 Solvent10% Transmission (nm)100% Transmission (nm) Acetone Acetonitrile Benzene Carbon Tetrachloride Cyclohexane Diethyl ether Dimethyl sulfoxide Ethanol Hexane Propan-2-ol Tetrahydrofuran Transmission characteristics of various solvents Measured for a 1cm path length of pure solvent

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48 Photochemical synthesis of oxetans Paternò-Büchi Reaction

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108 Norish Type I Processes of Ketones Basic Concepts

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125 Norish type II photoelimination of ketones: Cleavage of 1,4-biradicals formed by γ - hydrogen abstraction

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164 JACS, 1977, 99,

165

166

167

168

169 Mechanism I

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282 Bioluminescence Artistic rendering of bioluminescent Antarctic krillAntarctic krill Fireflies Firefly luciferin

283 Image of bioluminescent red tide event of 2005 at a beach in Carlsbad California showing brilliantly glowing crashing wavesred tide containing billions of Lingulodinium polyedrum dinoflagellatesLingulodinium polyedrumdinoflagellates

284

285

286

287 Photochemical aromatic substitution reaction

288

289

290

291

292

293

294

295

296

297

298

299

300 Photochemical reactions with singlet Oxygen

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321 Photo removable protecting groups

322

323

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

346

347

348

349

350

351

352

353

354

355

356

357

358

359

360

361

362

363

364


Download ppt "Organic photochemistry and pericyclic reactions (CY50003) 3-0-0."

Similar presentations


Ads by Google