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Molecular Orbitals and Ultraviolet Spectroscopy

Estimated value from unconjugated dienes or t lce the value for 1 -butene [Pg.525]

So now we have two measures of the energetic value of conjugation in 1,3-butadiene, and they are remarkably close to each other. The first is the height of the barrier to rotation about the C(2)—C(3) bond (4-5 kcal/mol), and the second is the lowering of the heat of hydrogenation of a conjugated diene relative to that of an unconjugated diene ( 3.6 kcal/mol). [Pg.525]

Overlap between middle carbons of a conjugated diene has structural consequences. The central sigma bond is slightly shorter than a normal carbon-carbon single bond. The magnitude of the conjugative stabilization is small, about 4 kcal/mol. [Pg.525]

In the early days of organic chemistry, there were two extraordinarily difficult general problems. One was to separate mixtures into pure compounds, and the other was to determine the structures of the compounds once pure samples were obtained. How simple these problems seem Yet, much of the mechanistic and synthetic organic chemistry of the last decades would have been quite impossible without the progress in solving these two old difficulties. We will have little to do with separation techniques in this book (your laboratory will take another approach), but we must certEunly spend some time here on structure determination. [Pg.525]

CHAPTER 12 Dienes and the Allyl System 2p Orbitals in Conjugation [Pg.526]


Up-to-Date Treatment In addition to the classical reactions, this book covers many techniques and reactions that have more recently gained wide use among practicing chemists. Molecular-orbital theory is included early and used to explain electronic effects in conjugated and aromatic systems, pericyclic reactions, and ultraviolet spectroscopy. Carbon-13 NMR spectroscopy is treated as the routine tool it has become in most research laboratories, and the DEPT technique is included in this edition. Many of the newer... [Pg.1297]

Ultraviolet photoelectron spectroscopy (UPS) results have provided detailed infomiation about CO adsorption on many surfaces. Figure A3.10.24 shows UPS results for CO adsorption on Pd(l 10) [58] that are representative of molecular CO adsorption on platinum surfaces. The difference result in (c) between the clean surface and the CO-covered surface shows a strong negative feature just below the Femii level ( p), and two positive features at 8 and 11 eV below E. The negative feature is due to suppression of emission from the metal d states as a result of an anti-resonance phenomenon. The positive features can be attributed to the 4a molecular orbital of CO and the overlap of tire 5a and 1 k molecular orbitals. The observation of features due to CO molecular orbitals clearly indicates that CO molecularly adsorbs. The overlap of the 5a and 1 ti levels is caused by a stabilization of the 5 a molecular orbital as a consequence of fomiing the surface-CO chemisorption bond. [Pg.951]

The molecular orbital theory of polyatomic molecules follows the same principles as those outlined for diatomic molecules, but the molecular orbitals spread over all the atoms in the molecule. An electron pair in a bonding orbital helps to bind together the whole molecule, not just an individual pair of atoms. The energies of molecular orbitals in polyatomic molecules can be studied experimentally by using ultraviolet and visible spectroscopy (see Major Technique 2, following this chapter). [Pg.247]

Ultraviolet-visible spectroscopy (UV = 200 - 400 nm, visible = 400 - 800 nm) corresponds to electronic excitations between the energy levels that correspond to the molecular orbital of the systems. In particular, transitions involving n orbital and ion pairs (n = non-bonding) are important and so UV/VIS spectroscopy is of most use for identifying conjugated systems which tend to have stronger absorptions... [Pg.79]

The preparation and study of tautomers derived from 2-(2 -pyridyl)indole, 2-(2 -pyrrolo)[l,8]naphthyridine, and related heterocycles has been undertaken using ultraviolet (UV) and nuclear magnetic resonance (NMR) spectroscopy and also by molecular orbital (MO) calculations <1998JOC4055>. [Pg.714]

Ultraviolet photoelectron spectroscopy (UPES) probes the valence band in the solid or the molecular orbitals in adsorbed species. The technique has no direct analytical potential but gives information on the local geometry at an adsorption site and on electronic structure. [35]... [Pg.560]


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Molecular orbitals spectroscopy

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Ultraviolet spectroscopy

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