Dienes


Also found in: Dictionary.

Dienes

 

(diolefins), unsaturated hydrocarbons having two double bonds. Depending on the mutual positions of the double bonds in the molecule, three types of dienes are distinguished: (1) dienes with isolated bonds, for example, pentadiene-1,4

and other dienes of the type

with chemical properties resembling those of olefins; (2)

dienes with adjacent double bonds Dienes forming

the class of allenes; (3) dienes with conjugated (alternating) double bonds, for example, 1,3-butadiene (divinyl)

2-methyl-butadiene-1,3 (isoprene)

CH2=C(CH3)—CHCH2

2-chloro-butadiene-1,3 (chloroprene)

CH2=CCl—CH—CH2

and cyclopentadiene

Ordinarily the term “diene” implies compounds with conjugated double bonds. In such compounds, the π bonds are conjugated and a single π-electron cloud is formed, giving rise to an increase in the energy of formation of the molecule, some averaging of the distances between the carbon atoms, the high polarizability of the molecule, and the ability of the molecule to undergo not only ordinary addition reactions at double bonds (1,2-addition), but also addition to the ends of the conjugated system (1,4-addition). Thus a bromine molecule adds to butadiene-1,3 to give 3,4-dibromobutene-l and l,4-dibromobutene-2:

Diene synthesis of the 1,4-addition type. Conjugated dienes (for example, butadiene, isoprene, and chloroprene) readily polymerize and copolymerize forming highly elastic polymers and copolymers. Stereospecific polymerization of isoprene yields a rubber whose structure is identical to that of natural rubber.

B. L. DIATKIN

References in periodicals archive ?
In 1913 Karl Rudolf Dienes successfully set his sights on solving difficult slitting related issues within the paper and converting industries.
Total serum cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglycerides (TG), PON and ARE activities and conjugated dienes levels were measured.
Dienes (1992, 1994a) means that it is not information itself in HMI studies that is considered as a resource or a product, but the goods and services (including the rendering of nondurable signals) that carry/convey information by carrying recorded, standard uniform signals.
Among other previously unseen images is a De Dienes shot taken of Monroe when she was 23 in a rare moment, where she was without make-up, the Telegraph reported.
The results showed that cowpea, black tea, green tea, rice bran and fenugreek ethanol extracts inhibited the formation of conjugated dienes by 92.
Ms Dienes was born and educated in New Zealand before moving to Winchester Cathedral as organ scholar in 1991.
A few years later, de Dienes photographed Marilyn during a New York publicity tour for "Love Happy.
Monroe, who died 40 years ago this month, is pictured when she was just 19 by photographer Andre de Dienes.
In his lecture, Suzuki gave an historical perspective of his reaction in the context of progress in boron chemistry, developed the theme of use of organoboron coupling reactions for the synthesis of dienes and biaryls, and, concentrating on work from other laboratories, provided an up-to-date report on the numerous applications of the Suzuki reaction inbioactive molecule and natural product synthesis.
Dienes, Emilian Dudas, and Tony Gherghetta wondered what would happen if they uncurled one or more of the extra dimensions in string theory to [10.
There are a lot of Hercules engines in use around the world," said jack Dienes, a former Hercules president who now serves as Hercules Engine Components president.