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One is trans-1,2-diphenylethylene, called (E)-stilbene or trans-stilbene. The second is cis-1,2-diphenylethylene, called -stilbene or cis-stilbene, and is sterically hindered and less stable because the steric interactions force the aromatic rings out-of-plane and prevent conjugation. [4]
For stilbene and other chemicals containing a double-bond linker between the two aromatic rings, the excited structure can undergo reversible cis-trans isomerization. Although only cis structures can undergo the cyclization step themselves, trans structures can isomerize in situ and then cyclize. [2]
Z)-Stilbene is a diarylethene, that is, a hydrocarbon consisting of a cis ethene double bond substituted with a phenyl group on both carbon atoms of the double bond. The name stilbene was derived from the Greek word stilbos , which means shining.
Very often, cis–trans stereoisomers contain double bonds or ring structures. In both cases the rotation of bonds is restricted or prevented. [4] When the substituent groups are oriented in the same direction, the diastereomer is referred to as cis, whereas when the substituents are oriented in opposing directions, the diastereomer is referred to as trans.
Resveratrol (3,5,4'-trihydroxystilbene) is a stilbenoid, a derivative of stilbene. [6] It exists as two geometric isomers: cis-(Z) and trans-(E), with the trans-isomer shown in the top image. Resveratrol exists conjugated to glucose. [40] The trans-form can undergo photoisomerization to the cis-form when exposed to ultraviolet irradiation. [41 ...
Two major classes are trans–cis (or E–Z) conversion, and open-closed ring transition. Examples of the former include stilbene and azobenzene . This type of compounds has a double bond , and rotation or inversion around the double bond affords isomerization between the two states. [ 13 ]
In E-Z isomerization, the thermal equilibrium lies well towards the trans-form because of its lower energy (~15 kJ mol −1 in stilbene). [3] The activation energy for thermal E-Z isomerization is 150–190 kJ mol −1 for stilbene, meaning that temperatures above 200°C are required to isomerize stilbene at a reasonable rate, but most ...
For instance, although cis-stilbene is "uphill" from trans-stilbene in a thermodynamic sense, irradiation of trans-stilbene results in a mixture that is predominantly the cis isomer. [2] As an extreme example, irradiation of benzene at 237 to 254 nm results in formation of benzvalene , an isomer of benzene that is 71 kcal/mol higher in energy ...