Names, valency

This value corresponded to an eightfold enhancement as compared to corresponding monovalent lactoside derivative under the same conditions. However, an increase in the branching of the dendron (namely valency) provided only a modest increase in the potency of the ligand, corresponding to a rather constant relative potency per lactose, regardless of the number of peripheral epitopes. 

Quantum mechanics provide many approaches to the description of molecular structure, namely valence bond (VB) theory (8-10), molecular orbital (MO) theory (11,12), and density functional theory (DFT) (13). The former two theories were developed at about the same time, but diverged as competing methods for describing the electronic structure of chemical systems (14). The MO-based methods of calculation have enjoyed great popularity, mainly due to the availability of efficient computer codes. Together with geometry optimization routines for minima and transition states, the MO methods (DFT included) have become prevalent in applications to molecular structure and reactivity. 

It is important to learn the names and valences of the five most common polyatomic ions nitrate, carbonate, chlorate, sulfate, and phosphate. These ions form many of the chemicals in nature and in common use. While the task seems overwhelming, it may help to learn the "big five" using a mnemonic, or memory aid. You can use the following mnemonic to remember their names, valences, and number of oxygen atoms ... 

Name Valency Symbol Name Valency Symbol... 

The name valence bond model arises from the fact that only valence electrons are considered. 

But since atoms can also exhibit accidental degeneracy, one could pose the following question can we talk about resonance in atoms At first sight this could be considered a totally meaningless question. After all, the resonance concept is intimately related to the VB-type methods and these should apply only to molecules, as the name valence-bond clearly suggests. However, the common belief that VB methods can only be applied to molecules is a consequence of a major historical mistake, as will be briefly shown. 

Name Valence Illustrative compound Ionic Nonionic ... 

Table 5.1 Molecular properties (number, name, molar volume N = v/h, architecture) and their segments (united atoms. A) (name, valence v), and relative dielectric permittivity e used in the SCF calculations. Here, t is the number of segments in the tail of the surfactantand Tis the number of V/segments around a central ion these parameters are varied.

Empirical conformational energy program for peptides (ECEPP) is the name of both a computer program and the force field implemented in that program. This is one of the earlier peptide force fields that has seen less use with the introduction of improved methods. It uses three valence terms that are fixed, a van der Waals term, and an electrostatic term. 

UFF stands for universal force held. Although there have been a number of universal force helds, meaning that they include all elements, there has only been one actually given this name. This is the most promising full periodic table force held available at this time. UFF is most widely used for systems containing inorganic elements. It was designed to use four valence terms, but not an electrostatic term. 

An older, but still used, notation specihes how many contractions are present. For example, the acronym TZV stands for triple-zeta valence, meaning that there are three valence contractions, such as in a 6—311G basis. The acronyms SZ and DZ stand for single zeta and double zeta, respectively. A P in this notation indicates the use of polarization functions. Since this notation has been used for describing a number of basis sets, the name of the set creator is usually included in the basis set name (i.e., Ahlrichs VDZ). If the author s name is not included, either the Dunning-Hay set is implied or the set that came with the software package being used is implied. 

There are several issues to consider when using ECP basis sets. The core potential may represent all but the outermost electrons. In other ECP sets, the outermost electrons and the last filled shell will be in the valence orbital space. Having more electrons in the core will speed the calculation, but results are more accurate if the —1 shell is outside of the core potential. Some ECP sets are designated as shape-consistent sets, which means that the shape of the atomic orbitals in the valence region matches that for all electron basis sets. ECP sets are usually named with an acronym that stands for the authors names or the location where it was developed. Some common core potential basis sets are listed below. The number of primitives given are those describing the valence region. 

SBKJC VDZ Available for Li(4.v4/>) through Hg(7.v7/ 5d), this is a relativistic basis set created by Stevens and coworkers to replace all but the outermost electrons. The double-zeta valence contraction is designed to have an accuracy comparable to that of the 3—21G all-electron basis set. Hay-Wadt MB Available for K(5.v5/>) through Au(5.v6/ 5r/), this basis set contains the valence region with the outermost electrons and the previous shell of electrons. Elements beyond Kr are relativistic core potentials. This basis set uses a minimal valence contraction scheme. These sets are also given names starting with LA for Los Alamos, where they were developed. 

Radicals derived from monocyclic substituted aromatic hydrocarbons and having the free valence at a ring atom (numbered 1) are named phenyl (for benzene as parent, since benzyl is used for the radical C5H5CH2—), cumenyl, mesityl, tolyl, and xylyl. All other radicals are named as substituted phenyl radicals. For radicals having a single free valence in the side chain, these trivial names are retained ... 

Otherwise, radicals having the free valence(s) in the side chain are named in accordance with the rules for alkanes, alkenes, or alkynes. 

The name phenylene o-, m-, or p-) is retained for the radical —C5H4—. Bivalent radicals formed from substituted benzene derivatives and having the free valences at ring atoms are named as substituted phenylene radicals, with the carbon atoms having the free valences being numbered 1,2-, 1,3-, or 1,4-, as appropriate. 

Radicals having three or more free valences are named by adding the suffixes -triyl, -tetrayl, etc. to the systematic name of the corresponding hydrocarbon. 

Radicals from Ring Systems. Univalent substituent groups derived from polycyclic hydrocarbons are named by changing the final e of the hydrocarbon name to -yl. The carbon atoms having free valences are given locants as low as possible consistent with the fixed numbering of the... 

Many trivial names exist for acids these are listed in Table 1.11. Generally, radicals are formed by replacing -ic acid by -oyL When a trivial name is given to an acyclic monoacid or diacid, the numeral 1 is always given as locant to the carbon atom of a carboxyl group in the acid or to the carbon atom with a free valence in the radical RCO—. 

The prefix sila- designates replacement of carbon by silicon in replacement nomenclature. Prefix names for radicals are formed analogously to those for the corresponding carbon-containing compounds. Thus silyl is used for SiH3—, silyene for —SiH2—, silylidyne for —SiH<, as well as trily, tetrayl, and so on for free valences(s) on ring structures. 

Other Polyatomic Anions. Names for other polyatomic anions consist of the root name of the central atom with the ending -ate and followed by the valence of the central atom expressed by its oxidation number. Atoms and groups attached to the central atom are treated as ligands in a complex. 

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