The additivity of group properties

A BENSON group consists of an atom of valency of at least 2 and of atoms or certain groups of atoms which are bound to it. 

In order to represent these groups, first of all the polyvalent atom is indicated followed by a hyphen, and it is followed by the atoms or the groups of bound atoms in brackets with an index which indicates the number of times each ligand occurs. 

The BENSON groups are shown using the following notations  

The following equivalences are permitted between certain groups of hydrocarbons and other groups  

CO represents a carbonyl group, N a trivalent nitrogen atom, a monovalent atom of nitrogen of the azo type, Nj a monovalent nitrogen of the type imino, O a divalent oxygen, S a divalent sulphur, SO2 a monovalent group. 

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Benson [15] has created and developed a general method of calculation of the values of thermochemical and kinetic parameters based on a systematic use of the additivity of group properties on the one hand and the activated complex theory on the other. Other methods for estimating a priori kinetic parameters have recourse to structural analogies or semi-empirical correlations. 

The study of the molar volumes of the normal hydrocarbons provided the earliest example of the additivity of group properties (Kopp 1855). The experimentally determined heats of formation for the same homologous series of molecules, CH3(CH2)mCH3, also obey a group additivity scheme (Franklin 1949 Prosen 1946 Benson 1968 Pittam and Pilcher 1972). It is possible to fit the experimental heats of formation for this series, beginning with m = 0, with the expression,... 

This method consists of a first phase using the additivity of group properties. The values of S and obtained during this first phase are then improved by different... 

If S is a single atom or a group of atoms with the bonds attached to the same atom (such as a CHi group), then we have the additivity of bond properties, liie first-order approximation, as given by Eq. (3). 

Alternatively, for many classes of compounds the heats of formation can be estimated through additivity of bond properties or group additivity rules [32], Let s take a simple example using the additivity of bond properties to estimate the heat of formation of some species A. Suppose we know (1) the heat of formation of a related compound ABR, where B is the atom to which A is bonded and R is the rest of the molecule, (2) the heat of formation of BR, and (3) that for a series of other molecules in which a A-B bond occurs the A-B bond-dissociation-energy is nearly constant, and we assign it the value B.D.E.(A-B) J. Now consider the endothermic reaction... 

Covalent modification-. The additions of groups to proteins or deletions from proteins, usually causing a change in the protein properties. 

The development of group additivity methods is very similar to the development of a QSPR method. Group additivity methods can be useful for properties that are additive by nature, such as the molecular volume. For most properties, QSPR is superior to group additivity techniques. 

Metallurgy. The strong affinity for oxygen and sulfur makes the rare-earth metals useflil in metallurgy (qv). Mischmetal acts as a trap for these Group 16 (VIA) elements, which are usually detrimental to the properties of steel (qv) or cast iron (qv). Resistance to high temperature oxidation and thermomechanical properties of several metals and alloys are thus significantly improved by the addition of small amounts of mischmetal or its siUcide (16,17). 

The Ekestone group also polymerized 1,3-butadiene to give an extremely high mol wt polybutadiene of 70% cis-1 4 stmcture. In thek research, they purposefully avoided the preparation of vinyl stmctures in both polyisoprene and polybutadiene since it was beheved that vinyl groups adversely affected tke performance. Since natural mbber was 99.9% cis-1 4 stmcture and had superior properties, they beheved that a 1,4 stmcture was necessary for acceptable physical properties. The addition of polar compounds to the hthium-catalyzed polymerization of butadiene changes the microstmcture from the 90% tij -l,4 stmcture to a mixed cis-1 4 and trans-1 4 microstmcture. 

The interaetion of PVP for various moleeular masses (8T0 - 360T0 ) with 3 groups of organie reagents sueh as triphenylmethane, trioxyfluorone and azodyes is established with the methods of UV-, VIS- and IR- speetroseopy. The ehanges of speetroseopie properties of dyes at addition of polymer ar e shown in shift of maximum of absorption bands, displaeement of reagent dissoeiation. The influenee of moleeular masses of polymer on properties of azodye-PVP adduets is studied. 

The two-component waterborne urethanes are similar in nature to the one-component waterborne urethanes. In fact, many one-component PUD s may benefit from the addition of a crosslinker. The two-component urethanes may have higher levels of carboxylic acid salt stabilizer built into the backbone than is actually needed to stabilize the urethane in water. As a result, if these two-component urethane dispersions were to be used as one-component adhesives by themselves (without crosslinker), they would show very poor moisture resistance. When these two-component urethane dispersions are used in conjunction with the crosslinkers listed in Fig. 8, the crosslinkers will react with the carboxylic pendant groups built into the urethane, as previously shown in the one-component waterborne urethane section. This accomplishes two tasks at the same time (1) when the crosslinker reacts with the carboxylic acid salt, it eliminates much of the hydrophilicity associated with urethane dispersion, and (2) it crosslinks the dispersion, which imparts solvent and moisture resistance to the urethane adhesive (see phase V in Fig. 5). As a result of crosslinking, the physical properties may be modified. For example, the results may be an increase in tensile properties and a decrease in elongation. Depending upon the level of crosslinking, the dispersion may lose the ability to be repositionable. (Many of the one-component PUD s may... 

An EB-curable struetural adhesive formulation usually eonsists of one or more crosslinkable oligomeric resins or prepolymers, along with such additives as reactive diluents, plasticizers, and wetting agents. The oligomer is an important component in terms of the development of mechanical properties. The adhesive and cohesive properties depend on the crosslink density, chemical group substitution, and molecular organization within the polymer matrix. Adhesion is achieved... 

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