Chemical group

Macromolecular reactions proceed more or less similarly to those of low-molecular-weight compounds. Special features are seen through the neighboring group effect and the whereabouts of the by-products.  

The reactivity of macromolecular and low-molecular-weight groups is about the same when neighboring group effects are taken into consideration. 

Isopropyl acetate, and not ethyl acetate or vinyl acetate, is thus the more suitable model compound for considering the hydrolysis of poly(vinyl acetate) with sodium hydroxide in acetone/water (75 25) at 30°C, as can be seen from the rate constants  

If there is only a small number of reactive groups per macromolecule, the environment of these groups is not changed as the reaction proceeds. The macromolecular chain simply acts as a diluent. Of course, neighboring group effects can also play a role, especially if five- and six-membered cyclic transition states can be formed. An example of this is the partial imidization of poly(methacrylamide) at temperatures above 65°C  

Even with a very low macromolecular concentration, the reactive groups are present at a quite high local concentration, since they are locally confined by being attached to the macromolecule. Most macromolecules form coils in solution (see Chapter 4). The concentration of reactive groups is very high within the coils it is virtually zero outside. 

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A substantial fraction of the named enzymes are oxido-reductases, responsible for shuttling electrons along metabolic pathways that reduce carbon dioxide to sugar (in the case of plants), or reduce oxygen to water (in the case of mammals). The oxido-reductases that drive these processes involve a small set of redox active cofactors , that is, small chemical groups that gain or lose electrons. These cofactors include iron porjDhyrins, iron-sulfur clusters and copper complexes as well as organic species that are ET active. 

American Cyanimid Co. Leeben Color, Div. of Tricon Colors, Inc. International Dyestuffs Cotp. Hilton-Davis Chemical Group of Sterling Dmg, Inc. 

Hoechst-Celanese Chemical Group International Product Index, Sept., 1991 Material S afety Data Sheets, Hoechst-Celanese, Corp., Dallas, Tex., 1991. 

Butane. Butane LPO has been a significant source for the commercial production of acetic acid and acetic anhydride for many years. At various times, plants have operated in the former USSR, Germany, Holland, the United States, and Canada. Only the Hoechst-Celanese Chemical Group, Inc. plants in Pampa, Texas, and Edmonton, Alberta, Canada, continue to operate. The Pampa plant, with a reported aimual production of 250,000 t/yr, represents about 15% of the 1994 installed U.S. capacity (212). Methanol carbonylation is now the dominant process for acetic acid production, but butane LPO in estabhshed plants remains competitive. 

MAK is used as a high soHds coating solvent (163) and in fragrances. It is available in the United States from Eastman (Kingsport, Teimessee), International Chemical Group (La Mesa, California) (47), and Union Carbide (South Charleston, West Virginia), and was priced at 1.36/kg in October 1994. 

Other commonly occurring chemical groups ia essential oils iaclude aromatics such as P-phenethyl alcohol, eugenol, vanillin, ben2aldehyde, cinnamaldehyde, etc heterocycHcs such as iadole (qv), pyra2iaes, thia2oles, etc hydrocarbons (Liaear, branched, saturated, or unsaturated) oxygenated compounds such as alcohols, acids, aldehydes, ketones, ethers and macrocyclic compounds such as the macrocyclic musks, which can be both saturated and unsaturated. 

M. Novotny, Environmentally Friendly Pigments, presented at Industrial Inorganic Chemicals Group, Royal Society of Chemistry, London, Jan. 12, 1994. 

Hoechst Celanese Corp., Specialty Chemical Group Cookson Pigment, Inc. 

If an adsorbed chemical group (anchor) is more strongly bound to the surface than a solvent molecule would be at that site, an equiHbrium expression may be written for the displacement of solvent by adsorbate. Adsorption is particularly strong if the chemical nature of the adsorbed group is similar to that of the particle surface for example, in aqueous systems perfluoroalkane groups adsorb weU on polytetrafluoroethene particles and aromatic polyethene oxides adsorb weU on polystyrene. 

Ethyl Chemicals Group, Product Bulletin, CG-220R (3 j89), Industrial Chemicals Division Products, Ethyl Corporation, Baton Rouge, La., Mar. 1989. 

Sulfur Products Handbook on Sulfur Monochloride and Sulfur Chloride, Bulletin SPE-SUL-HB 10/9, Oxychem Basic Chemicals Group, Occidental Chemical Corp., Dallas, Tex., 1993, p. 3. 

HinjlAcetate A Guide to Safety and Handling, compiled by E. I. duPont de Nemours and Co., Inc., Hoechst Celanese Chemical Group, Inc.,... 

In addition to the restrictions on their mobiHty caused by steric and polar interactions between chemical groups, the protein molecules in wool fibers are covalentiy cross-linked by disulfide bonds. Permanent setting only occurs if these disulfide bonds are also rearranged to be in equiHbrium with the new shape of the fiber. Disulfide bond rearrangement occurs only at high temperature (>70° C) in wet wool and at even higher temperatures (above 100°C) in... 

Sodium tetrabydroborate [16940-66-2] NaBH, more commonly called sodium borobydride, is tbe most widely used commercial boron bydride. Tbe largest manufacturer is Morton International Specialty Chemicals Group, which has two plants in the United States and one in Europe (1). Oy Nokia Ab Chemicals (FN) (2) also produces commercial quantities. Smaller producers include Farbenfabrik Bayer A.G. and ChemetaH Gmbh in Germany (2). 

Sodium Borohjdride Digest, Morton International, Specialty Chemicals Group, Danvers, Mass., 1989. 

BASF, Fibers Division, Dispersions Textile Chemicals Group Burlington Chemical Co. 

Covalent Bonds. Fiber-reactive dyes, ie, dyestuff molecules containing reactive groups, are adsorbed onto the fiber and react with specific sites (chemical groups) in the fiber polymer to form covalent bonds. The reaction is irreversible, so active dye is removed from the equiUbrium system (it becomes part of the fiber) and this causes more dye to adsorb onto the fiber to re-estabflsh the equiUbrium of active dye between fiber and aqueous dyebath phases (see Dyes, reactive). 

A reactive dye for ceUulose contains a chemical group that reacts with ionized hydroxyl ions in the ceUulose to form a covalent bond. When alkaH is added to a dyebath containing ceUulose and a reactive dye, ionization of ceUulose and the reaction between dye and fiber is initiated. As this destroys the equihbrium more dye is then absorbed by the fiber in order to re-estabUsh the equUibrium between active dye in the dyebath and fiber phases. At the same time the addition of extra cations, eg, Na+ from using Na2C02 as alkaH, has the same effect as adding extra salt to a direct dye. Thus the addition of alkaH produces a secondary exhaustion. 

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