Pi bonds conjugated

A characteristic feature of conjugated pi-bond networks is that each pi bond 7ta lies adjacent (vicinal, s-cis or s-trans) to a coplanar pi bond 7tb, a pi-type lone pair nb, or a pi-type vacancy nb (unfilled valence p orbital), e.g.,... 

Of alkane chains and conjugated pi bond structures, which chemical structure do molecules that absorb UV light have ... 

A structural feature that many molecules that absorb UV light have is a conjugated pi bond skeleton. 

Since the discovery of doped polyacetylene, a range of polymer-intense semiconductor devices have been studied including normal transistors and field-effect transistors (FETs), and photodiodes and light-emitting diodes (LEDs). Like conductive polymers, these materials obtain their properties due to their electronic nature, specifically the presence of conjugated pi-bonding systems. 

Pericyclic reactions are commonly divided into three classes electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. An electrocyclic reaction forms a sigma bond between the end atoms of a series of conjugated pi bonds within a molecule. The 1,3-butadiene to cyclobutene conversion is an example, as is the similar reaction of 1,3,5-hexatriene to form 1,3-cyclohexadiene ... 

Electrocyclic reaction (Section 22.3) A peri-cyclic reaction that forms a sigma bond between the end atoms of a series of conjugated pi bonds within a molecule. 

The structure must be cyclic, containing some number of conjugated pi bonds. 

This coal of intermediate rank has rather extensive polynuclear formation and polar functional groups. Thus we would expect dispersion, polarizability, and dipolar interactions between the substrate entities and the sorbate molecules. The polar portion of the substrate as well as the highly conjugated pi-bonded electrons most assuredly are involved in the sorption process. Such a concept is quite suggestive and compatible with the polarization theory for sorption processes (9, 13, 14), where the energetics are predicted to follow the relationship... 

OLEDs are based on certain organic small molecules or polymers that behave as diode semiconductors with an applied current. The organic materials derive their semiconducting properties from their highly conjugated pi-bond molecular structures that allow electrons to flow within or across the molecular bonds. Whether... 

The location of the OH leaving group in a position that is beta to a carbonyl, along with the formation of a stable, conjugated pi bond, makes this reaction much easier than a dehydration of an ordinary alcohol. The dehydration of an aldol product requires much milder reaction conditions than a typical alcohol, and can even occur spontaneously at room temperature. For example, in the reaction of benzaldehyde with acetone, the double aldol product shown is the only one isolated the presence of the two benzene rings makes the newly formed pi bonds highly conjugated and very stable. 

What is the MM3 enthalpy of formation at 298.15 K of styrene Use the option Mark all pi atoms to take into account the conjugated double bonds in styrene. Is the minimum-energy structure planar, or does the ethylene group move out of the plane of the benzene ring ... 

In the limit that nearest-neighbor contributions dominate, such a one-center nb automatically leads to an approximate 21/2-fold increase in overlap and two-fold increase in interaction energy, compared with a two-center 7tb donor. A corresponding enhancement results when the pi-acceptor is reduced from two-center (7tb ) to one-center (nb ) form, i.e., a valence p-type vacancy. Unlike the intrinsically bidirectional character of conjugation between two pi bonds (7ta->-7tb, 7tb 7ta ), the interactions of a pi bond with a nonbonding center are intrinsically mono-directional and lead to uncompensated transfer of pi charge from one moiety to the other. 

Even cursory inspection will show that conjugation alters the properties of the participating pi bonds. For example, the vinyl 7tcc NBO of 6 is not homopolar as in ethylene, but instead becomes rather strongly polarized toward C2,... 

We first consider benzene, 17, the prototypical aromatic molecule. From the entries in Table 3.21 and comparisons analogous to Example 3.15, one can recognize that conjugative stabilizations in benzene are significantly stronger than those of comparable species in Table 3.19. Thus, on a per-pi-bond basis, the estimated stabilizations in benzene are 40.8 kcal mol-1, more than three times those of diene 2 (12.8 kcal mol-1), twice those of the acyclic triene 11 (20.3 kcal mol-1), and about 58% greater than the most strongly stabilized polyene, 16 (25.8 kcal mol-1). 

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