Position of substituents

The 6(CH) bending vibrations have been located between 1250 and 1000 cm and show varying frequencies as a function of the nature and the position of substituents (203). It is possible, however, that the SC(2,H mode is located near 1220 cm and suffers the weakest influence from 4-or 5-Substitution. 

Substituent in XC6H4CO2H Acidity of Some Substituted Benzoic Acids pKa for different positions of substituent X ... 

The position of substituents is indicated by numbers, with the lowest locant possible given to substituents. When a name is based on a recognized trivial name, priority for lowest-numbered locants is given to substituents implied by the bivial name. When only two substituents are present on a benzene ring, their position may be indicated by o- ortho-), m- meta-), and p- (para-) (and alphabetized in the order given) used in place of 1,2-, 1,3-, and 1,4-, respectively. 

The ortho para isomer ratio depends on several factors, including the nature of the diazo component, the nature of the solvent, the pH of the medium, the temperature of coupling, the presence of catalysts, and the position of substituents. Simple benzenediazonium compounds couple to... 

The nature and position of substituents on the arylidene ring markedly affect the ratio of addition products to cleavage products. As expected, electron-releasing substituents enhance the cleavage reaction. 

The oxazolo[3,4-a]azepinones 4, in which 5 7 ring fusion imparts considerable planarity and hence antiaromatic character on the ring system, undergo spontaneous dimerization.153 The mode of dimerization appears to depend on the nature and position of substituents. The unsubstituted system and the 9-chloro derivative 4 (R1 = Cl R2 = H) produce the exo.anti-dimers, e.g. 5, upon spray-vacuum pyrolysis at 300 C, whereas the 7-/ert-butyl, 7-bromo, 7-methyl, and 7,9-dichloro (4, R1 = R2 = Cl) compounds yield the exo,syn-dimcrs, e.g. 6. 

The other structural parameters, such as the ester group content, the presence, nature, and position of substituents on monomer units, and the number and nature of comonomers, are of less importance and do not modify this classification of hnear polyesters. 

Substituents replacing the hydrogen atom of an alcoholic hydroxy group of a saccharide or saccharide derivative are denoted as O-substituents. The 0- locant is not repeated for multiple replacements by the same atom or group. Number locants are used as necessary to specify the positions of substituents they are not required for compounds fully substituted by identical groups. Alternative periphrase names for esters, ethers, etc. may be useful for indexing purposes. For cyclic acetals see 2-Carb-28. 

The position of substituents on the ring and their relation to each other corresponds to the number of the carbon to which they are attached. 

These examples illustrate the issues that must be considered in analyzing the stereoselectivity of enolate alkylation. The major factors are the conformation of the enolate, the stereoelectronic requirement for an approximately perpendicular trajectory, the steric preference for the least hindered path of approach, and minimization of torsional strain. In cyclic systems the ring geometry and positioning of substituents are often the dominant factors. For acyclic enolates, the conformation and the degree of steric discrimination govern the stereoselectivity. 

Fluorescence. - A further report on the use of naphthalene phosphorus compounds for fluorescence derivatization concerns the dependence of fluorescence on the type and position of substituents on the naphthalene rings.141 It has been found that the... 

Quinolizine exists as a mixture of up to three species, namely the 2H-, 4H- and 9a/7-tautomers (17 and 18, respectively). This tautomeric equilibrium has been extensively studied in the case of tetramethyl quinolizine-1,2,3,4-tetracarboxylate, where, as previously mentioned, the 4/7-tautomer 17 has been shown to be thermodynamically more stable than the 9/7-species 18 through ab initio Hartree-Fock calculations. An interesting feature of these compounds is that the rate of the interconversion of the 9a//-tautomer 18 into the more stable 4//-cornpound 17 depends on the position of substituents in ring B <2003JST651>. 

Synjanti Prefixes that describe the relative positions of substituents with respect to the defined plane of a ring syn for the same side and anti for the opposite side (Fig. 1-35). 

As mentioned in Chapter 2, the introduction of the a- and co-side chains is controlled by the chirality at C-ll of 78 through 1,2-unft-induction. If the C-ll protected hydroxyl moiety of 78 is a-orientated (a and jt are adopted from carbohydrate chemistry, indicating the relative position of substituents), the newly... 

Korner s method org chem A method for determining the absolute position of substituents for positional isomers in benzene by the experimental production of positional isomers from a given disubstituted benzene. kor-norz, meth-3d ... 

Find the shortest path in atoms, irrespective of their nature, from the subunit of the highest seniority to the subunit of the same seniority (Rules 15,16), if present, or of the second highest seniority (Rules 13,14). Where paths of equal length are identified as shortest, the choice depends on the seniority of the remaining subunits and the number and positions of substituents ... 

The types and position of substituents at the silicon atom are denoted at the beginning of the name. If all the substituents are the same, their position is not necessary to be shown. In this case, the substituent name is preceded by a prefix per- or the total number of substituents is indicated for example, permethyl- , hexaethyl- , octaethyl- , etc. 

In 1996, Wu et al. reported the isolation of clausine E (25) from the stem bark of C. excavata (46). One year later, Ito et al. reported the isolation of the same alkaloid from the same source and named it clauszoline-I (25) (47). This alkaloid showed inhibition of rabbit platelet aggregation and caused vasocontraction. The UV, IR, and H-NMR spectra were similar to those of mukoeic acid (10) with respect to the position of substituents. The presence of a carbomethoxy group at C-3 was indicated by an IR band at 1703 cm . Moreover, two significant mass fragments at m/z 210 (M —OMe) and 182 (M —COOMe) confirmed the presence of a carbomethoxy group. On the basis of these spectral data, structure 25 was assigned to clausine E (clauszoline-I) (Scheme 2.6). 

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