- Carbomer
In
organic chemistry , a carbomer is an expandedmolecule obtained by insertion of a C2 unit in a given molecule ["Carbomers. I. A general concept of expanded molecules" Remi ChauvinTetrahedron Letters Volume 36, Issue 3 , 16 January 1995, Pages 397-400 doi|10.1016/0040-4039(94)02275-G ] . Carbomers differ from their templates in size but not in symmetry when each C–C single bond is replaced by at least onealkyne bond, and when a double bond is replaced by anallene bond. The size of the carbomer will continue to increase when more alkyne bonds are introduced and for this reason carbomers are also called carbon-molecules, where "n" is the number of acetylene or allene groups in an n-expansion unit. This concept, devised by Remi Chauvin in 1995, is aimed at introducing new chemical properties for existing chemical motifs.:
Two representations exist for carbo-benzene (written as an [Cyclooctadecanonaene| [18] annulene] derivative: 1,2,4,5,7,8,I0,11,13,14,16,17-dodecadehydro [18] annulene), one has the aromatic core of
benzene expanded, and one has the hydrogensubstituent s expanded. The substituted benzene derivative hexaethynylbenzene is a known compound, ["Hexaethynylbenzene" Rainer Diercks, James C. Armstrong, Roland Boese, K. Peter C. Vollhardt. Hexaethynylbenzene. "Angewandte Chemie International". 1986; 25(3):268-269. DOI|10.1002/anie.198602681] and the core-expanded molecule also exists, although with the hydrogen atoms replaced byphenyl groups ["Synthesis of the first 3,6,9,15,18,18-hexa-substituted-1,2,4,5,7,8,10,11,13,14,16,17-dodecadehydro [18] annulenes with D6h-symmetry" Yoshiyuki Kuwatani, Naoto Watanabe and Ikuo UedaTetrahedron Letters Volume 36, Issue 1 , 2 January 1995, Pages 119-122 doi|10.1016/0040-4039(94)02181-A ] . The final step in itsorganic synthesis isorganic oxidation of the triol withstannous chloride andhydrochloric acid indiethyl ether .:
The
proton NMR spectrum for this compound shows that the phenyl protons are shifted downfield compared to a proton position in benzene itself (chemical shift position for the ortho proton is 9.49 ppm), suggesting the presence of adiamagnetic ring current and thusaromaticity .The total carbomer of benzene with core and periphery expanded (C30H6) only exists
in silico ["Total carbo-Mer of Benzene, Its carbo-Trannulene Form, and the Zigzag Nanotube Thereof" Christine Lepetit, Chunhai Zou, and Remi ChauvinJ. Org. Chem. ; 2006; 71(17) pp 6317 - 6324; (Article) DOI|10.1021/jo052551j] .:
Calculations predict a planar D6h structure with
bond length s similar to the other two carbobenzenes. Its non-planarisomer is called "hexaethynyl-carbo- [6] trannulene" - a pun on the all-"cis"annulene s - and resembles acyclohexane ring. This hypothetical molecule is predicted to be more energetic by 65 kcal/mol.Other carbomer meanings
Carbomer is also a generic name for synthetic
polymer s ofacrylic acid used asemulsion stabilizers orthickening agent s in pharmaceuticals and cosmetic products. They may behomopolymer s of acrylic acid,crosslinked with anallyl ether pentaerythritol , allyl ether ofsucrose , or allyl ether ofpropylene .References
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