The Typing Rules

Atom types represent the chemical environment of an atom. The atom types associated with a given force field could be hard-wired to have specific values and meaning. HyperChem also allows flexible definitions of the atom types and the associated chemical environments. The chemical environment of an atom (a set of rules for defining a type) and the default rules are in a standard ASCII text file, chem.rul, included with HyperChem. You can modify this file and compile it in a binary form that HyperChem 

The syntax and semantics of the typing rules in a chem.rul file are included in the HyperChem Reference Manual. The following example illustrates their use. The five AMBER types for oxygen atoms shown above are defined in chem.rul by the following rules  

These rules are executed in order until a set of rules is satisfied. If all the rules fail then the last default type OS is assigned. The tests on neighboring lines are AND ed together and sets of tests (clauses) separated by blank lines are OR ed. 

Note that two different environments, although they might be distinguished by tests (such as for ether and ester) can share an atom type (such as OS). Arefinement of the AMBER force field would use separate types for these two along with different parameters for the different types. 

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Next to fire is type rule Osize. First, it fires using property 4b to establish properties 7a and 7b. Then using property 6b, properties 8a and 8b are established. The type rule Asize now fires three times. First, using properties 7a and 7b, and then using properties 8a and 8b the properties 9 and 10 are added to the WM. On the third firing property 11, that Pi and Q2 are the same size, is deduced. Facts 4b and 6 and property 11 permit Multiply to be invoked, resulting in fact 12 and property 12 being added to... 

The type rule Oproduct uses properties 4a, 6a, and 12 to establish property 14. The antecedents of the type rule EVector can now be matched by properties 14, 13, and 5b. This causes the rule to fire and add property 15 to the WM. The penultimate rule to be matched is CIExpan. Its antecedents are matched by properties 2, 3a and 15 resulting in property 16 being added to the WM. Finally, property 16 causes the goal rule to fire and execution to terminate. 

Erlenmeyer s rule This originally postulated that all unsaturaled alcohols of the types... 

This spectrum is called a Raman spectrum and corresponds to the vibrational or rotational changes in the molecule. The selection rules for Raman activity are different from those for i.r. activity and the two types of spectroscopy are complementary in the study of molecular structure. Modern Raman spectrometers use lasers for excitation. In the resonance Raman effect excitation at a frequency corresponding to electronic absorption causes great enhancement of the Raman spectrum. 

One may rationalize emulsion type in terms of interfacial tensions. Bancroft [20] and later Clowes [21] proposed that the interfacial film of emulsion-stabilizing surfactant be regarded as duplex in nature, so that an inner and an outer interfacial tension could be discussed. On this basis, the type of emulsion formed (W/O vs. O/W) should be such that the inner surface is the one of higher surface tension. Thus sodium and other alkali metal soaps tend to stabilize O/W emulsions, and the explanation would be that, being more water- than oil-soluble, the film-water interfacial tension should be lower than the film-oil one. Conversely, with the relatively more oil-soluble metal soaps, the reverse should be true, and they should stabilize W/O emulsions, as in fact they do. An alternative statement, known as Bancroft s rule, is that the external phase will be that in which the emulsifying agent is the more soluble [20]. A related approach is discussed in Section XIV-5. 

The fimdamental kinetic master equations for collisional energy redistribution follow the rules of the kinetic equations for all elementary reactions. Indeed an energy transfer process by inelastic collision, equation (A3.13.5). can be considered as a somewhat special reaction . The kinetic differential equations for these processes have been discussed in the general context of chapter A3.4 on gas kmetics. We discuss here some special aspects related to collisional energy transfer in reactive systems. The general master equation for relaxation and reaction is of the type [H, 12 and 13, 15, 25, 40, 4T ] ... 

The absolute measurement of areas is not usually usefiil, because tlie sensitivity of the spectrometer depends on factors such as temperature, pulse length, amplifier settings and the exact tuning of the coil used to detect resonance. Peak intensities are also less usefiil, because linewidths vary, and because the resonance from a given chemical type of atom will often be split into a pattern called a multiplet. However, the relative overall areas of the peaks or multiplets still obey the simple rule given above, if appropriate conditions are met. Most samples have several chemically distinct types of (for example) hydrogen atoms within the molecules under study, so that a simple inspection of the number of peaks/multiplets and of their relative areas can help to identify the molecules, even in cases where no usefid infonnation is available from shifts or couplings. 

Hiickel-type systems (such as Hilcfcel pericyclic reactions and suprafacial sigmatropic shifts) obey the same rules as for sigma electron. The rationale for this observation is clear If the overlap between adjacent p-electron orbitals is positive along the reaction coordinate, only the peraiutational mechanism can... 

Accepting the Longuet-Higgins rule as the basis for the search of conical intersection, it is necessary to look for the appropriate loop. The -type degeneracy of a Jahn-Teller system is removed by a nonsymmetric motion. 

After the definition of a reaction type, a scheme for the evaluation of the given reaction type can follow in the reaction rule. An entire hierarchy of evaluations can be implemented, from no evaluation at all to a full-fledged estimation of reaction kinetics [12 ... 

I he results of their calculations were summarised in two rules. The first rule states that at least one isomer C with a properly closed p shell (i.e. bonding HOMO, antibonding I. U.MO) exists for all n = 60 - - 6k (k = 0,2,3,..., but not 1). Thus Qg, C72, Cyg, etc., are in lhi-< group. The second rule is for carbon cylinders and states that a closed-shell structure is lound for n = 2p(7 - - 3fc) (for all k). C70 is the parent of this family. The calculations Were extended to cover different types of structure and fullerenes doped with metals. 

Let s compare the carbocation intermediates for addition of a hydrogen halide (HX) to an unsymmetrical alkene of the type RCH=CH2 (a) according to Markovnikov s rule and (b) opposite to Markovnikov s rule (a) Addition according to Markovnikov s rule... 

Kharasch called this the peroxide effect and demonstrated that it could occur even if peroxides were not deliberately added to the reaction mixture Unless alkenes are pro tected from atmospheric oxygen they become contaminated with small amounts of alkyl hydroperoxides compounds of the type ROOH These alkyl hydroperoxides act m the same way as deliberately added peroxides promoting addition m the direction opposite to that predicted by Markovmkov s rule... 

Although substitutive names of the type just described are preferred the lUPAC rules also permit ketones to be named by functional class nomenclature The groups attached to the carbonyl group are named as separate words followed by the word ketone The groups are listed alphabetically... 

Quaternary ammonium hydroxides un dergo elimination on being heated It is an anti elimination of the E2 type The regioselectivity of the Hofmann elimina tion IS opposite to that of the Zaitsev rule and leads to the less highly substi tuted alkene... 

The form that single atom type constants take is selected by setting the Registry/chem.ini parameter set entry 6-12AtomVDWFormat to one of RStarEpsilon, SigmaEpsilon or SlaterKirkwood. This specifies the combination rules that are used for the file pointed to by the 6-12AtomVDW entry in the Registry or the chem.ini file for the same parameter set. 

Newer, published CHARMM parameter sets override some of the combination rule generated parameters for some atom type pairs. These parameters are found in the file pointed to by the 6-12PairVDW entry for the parameter set, usually called npr.txt(dbf). The values of Ay and By for these are computed using equations (22) and (23) on page 178 by setting the 6-12PairVDWFormat entry to RStarEpsilon. 

This widespread conformity to the Gurvitsch rule constitutes powerful support for the capillary condensation hypothesis in relation to Type IV isotherms. It is perhaps hardly necessary to stress that in order to test data for conformity to the rule it is essential that the stage which corresponds to the complete filling of the pores shall be clearly identifiable—as in the... 

Evidence of a different kind is furnished by the fact that the Gurvitsch rule (p. 113) is often obeyed by systems showing Type I isotherms " the amounts of different adsorptives taken up by a given adsorbent, when expressed as a volume of liquid, agree within a few per cent. The order of agreement is illustrated by the typical examples in Table 4.1 for the adsorption of n-alkanes on ammonium phosphomolybdate, and in Table 4.2 which refers to a variety of adsorptives on a silica gel. It must be admitted, however, that there are cases where considerable deviations from the Gurvitsch mle are found, even though the isotherms are of Type 1. Thus, in Table 4.3 the variation in values of the saturation uptake is far outside... 

As is the case for vibrational transitions, electronic transitions are mostly of the electric dipole type for which the selection rules are as follows. 

During the adsorption or occlusion of various molecules, the micropores fill and empty reversibly. Adsorption in zeoHtes is a matter of pore filling, and the usual surface area concepts are not appHcable. The pore volume of a dehydrated zeoHte and other microporous soHds which have type 1 isotherms may be related by the Gurvitch rule, ie, the quantity of material adsorbed is assumed to fill the micropores as a Hquid having its normal density. The total pore volume D is given by... 

Each plant or laboratory should adopt definite rules and procedures for electrical iastahations and work. All iastahations should be ia accordance with the National Electrical Code (NEC) for the type of ha2ard, eg. Class I flammable gas or vapor Class II organic, metallic, or conductive dusts and Class III combustible fibers and the degree of process containment, eg. Division 1 open and Division 2 closed (67). Regardless of the flammabiUty of the materials ia the iastaHed operations, changes ia procedure involving use of such materials often occur, sometimes without concurrent alteration of the electrical iastaHation. 

To determine the size of the magnetic field to be used, the type and size of tramp iron to be removed must be known. A general rule of thumb for 13 to 25 mm balls or cubes is that a 0.1-T (1-kG) field is required at the suspension distance. For tramp iron 50 mm and larger, a 0.05—0.08-T (0.5—0.8-kG) field is required at the suspension distance. 

The general rule of thumb is that most tank facilities are subject to multiple authorities. When this is the case and the rules have ovedapping or even conflicting provisions, the facility must comply with all the requirements of the multiple authorities. In short, one authority s requirements does not preempt or even satisfy the requirements of the other agency even if they accomphsh exactiy the same thing. There are many examples of this type of inefficiency in regulations. 

Spill Prevention and Detection. It is far better to prevent a leak or a spik than to clean one. The fundamental rule of leak and spik prevention is to reduce the possibkity for contamination by directing resources as close to the source as possible (Fig. 11). In addition to increasing the effectiveness of a spik and leak prevention program, the costs are lower if the focus is placed on preventing the occurrence in the first place. Regulatory trend, however, is to requite methods that respond to leaks after they occur. In addition to being more costly, this type of requirement is often a disincentive to prevent the leaks in the first place, because of the additional cost. 

For a PVnr system of uniform T and P containing N species and 7T phases at thermodynamic equiUbrium, the intensive state of the system is fully deterrnined by the values of T, P, and the (N — 1) independent mole fractions for each of the equiUbrium phases. The total number of these variables is then 2 + 7t N — 1). The independent equations defining or constraining the equiUbrium state are of three types equations 218 or 219 of phase-equiUbrium, N 7t — 1) in number equation 245 of chemical reaction equiUbrium, r in number and equations of special constraint, s in number. The total number of these equations is A(7t — 1) + r -H 5. The number of equations of reaction equiUbrium r is the number of independent chemical reactions, and may be deterrnined by a systematic procedure (6). Special constraints arise when conditions are imposed, such as forming the system from particular species, which allow one or more additional equations to be written connecting the phase-rule variables (6). 

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