第八章 红外和核磁.ppt

* 8 * 8 * 8 * 8 * 8 * 8 * 8 * 8 * 8 * 8 * 2 * 3 * 4 * 5 * 5 * 5 * 5 200 220 240 260 280 1000 2000 Wavelength, nm lmax 230 nm emax 2630 Molarabsorptivity (e) UV Spectrum of cis,trans-1,3-cyclooctadiene Most stable p-electron configuration p-Electron configuration of excited state y1 y2 y3* y4* y1 y2 y3* y4* p?p* Transition in cis,trans-1,3-cyclooctadiene HOMO LUMO DE = hn p?p* Transition in Alkenes HOMO-LUMO energy gap is affected by substituents on double bond as HOMO-LUMO energy difference decreases (smaller DE), lmax shifts to longer wavelengths Methyl groups on double bond cause lmax to shift to longer wavelengths C C H H H H C C H H CH3 lmax 170 nm CH3 lmax 188 nm Extending conjugation has a larger effect on lmax; shift is again to longer wavelengths C C H H H H C C H H lmax 170 nm lmax 217 nm H C C H H H lmax 217 nm(conjugated diene) H C C H H C C H H H C C H CH3 H H C C H3C H C C H H lmax 263 nmconjugated triene plus two methyl groups Lycopene lmax 505 nm orange-red pigment in tomatoes 8.6 质谱 The mass of molecules may be measured?? Molecules of an unknown compound are ionised by impact with electron in a high vacuum ?? Ions thus produced are accelerated through an electric potential?? During the ionisation process, some ions can fragment to form smaller ions (daughter ions) Mass spectrometry Ions are separated according to m/z?? The beam of ions is directed at right angles into a magnetic field?? The force exerted on the ions by the magnetic field causes them to trace out a circular path whose radius depends on the mass and the charge of the ion. The charge is almost always 1+ 质谱 质谱 Example -methanol The heaviest ion is due to the molecular ion and results from loss of one electron from the parent molecule?? Since electrons are so light the mass of the molecular ion is effectively the same as that of the parent molecule?? Fragmentation may occur to give daughter ions that help determine the structure of the molecule A typical mass spectrum Feat