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Benzene has three aromatic π → π* transitions; two E-bands at 180 and 200 nm and one B-band at 255 nm with extinction coefficients respectively 60,000, 8,000 and 215. These absorptions are not narrow bands but are generally broad because the electronic transitions are superimposed on the other molecular energy states.
para-disub. benzene 800–860 strong alkynes: any 3300 medium aldehydes: any 2720 medium 2820 C═C acyclic C═C monosub. alkenes 1645 medium 1,1-disub. alkenes 1655 medium cis-1,2-disub. alkenes 1660 medium trans-1,2-disub. alkenes 1675 medium trisub., tetrasub. alkenes 1670 weak conjugated C═C dienes 1600 strong 1650 strong with benzene ...
In the simple aromatic ring of benzene, the delocalization of six π electrons over the C 6 ring is often graphically indicated by a circle. The fact that the six C-C bonds are equidistant is one indication that the electrons are delocalized; if the structure were to have isolated double bonds alternating with discrete single bonds, the bond would likewise have alternating longer and shorter ...
Benzene is a natural constituent of petroleum and is one of the elementary petrochemicals. Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon. Benzene is a colorless and highly flammable liquid with a sweet smell, and is partially responsible for the aroma of gasoline.
The nitrogen (N)-containing aromatic rings can be separated into basic aromatic rings that are easily protonated, and form aromatic cations and salts (e.g., pyridinium), and non-basic aromatic rings. In the basic aromatic rings, the lone pair of electrons is not part of the aromatic system and extends in the plane of the ring.
E 1 = α + 2β: 2β (E 2, E 3) and (E 4, E 5) are degenerate E 2 = α + β: HOMO E 3 = α + β: HOMO E 4 = α − β: LUMO E 5 = α − β: LUMO E 6 = α − 2β: Table 1. Hückel method results. Because α and β are negative, [8] orbitals are in order of increasing energy. HOMO/LUMO/SOMO = Highest occupied/lowest unoccupied/singly-occupied ...
Aniline absorbs in the K (220 - 250 nm) and the B (250 - 290 nm) bands exhibited by benzenoid compounds. The K and B bands arise from π to π* transitions as a result of the a group containing multiple bond being attached to the benzene ring. When dissolved in ethanol, λ max for aniline is 230 nm, but in dilute aqueous acid λ max is 203 nm ...
Band theory derives these bands and band gaps by examining the allowed quantum mechanical wave functions for an electron in a large, periodic lattice of atoms or molecules. Band theory has been successfully used to explain many physical properties of solids, such as electrical resistivity and optical absorption , and forms the foundation of the ...