Group, replacement

Electronegative substituents m a molecule can affect acidity even when they are not directly bonded to the lomzable proton Compare ethanol (CH3CH2OH) with a related compound m which a CE3 group replaces the CH3 group... 

The Lewis acid Lewis base idea also includes certain substitution reactions m which one atom or group replaces another... 

As discussed earlier in Section lOC.l, ultraviolet, visible and infrared absorption bands result from the absorption of electromagnetic radiation by specific valence electrons or bonds. The energy at which the absorption occurs, as well as the intensity of the absorption, is determined by the chemical environment of the absorbing moiety. Eor example, benzene has several ultraviolet absorption bands due to 7t —> 71 transitions. The position and intensity of two of these bands, 203.5 nm (8 = 7400) and 254 nm (8 = 204), are very sensitive to substitution. Eor benzoic acid, in which a carboxylic acid group replaces one of the aromatic hydrogens, the... 

In the examples, a nitro group is substituted for a hydrogen atom, and water is a by-product. Nitro groups may, however, be substituted for other atoms or groups of atoms. In Victor Meyer reactions which use silver nitrite, the nitro group replaces a hahde atom, eg, I or Br. In a modification of this method, sodium nitrite dissolved in dimethyl formamide or other suitable solvent is used instead of silver nitrite (1). Nitro compounds can also be produced by addition reactions, eg, the reaction of nitric acid or nitrogen dioxide with unsaturated compounds such as olefins or acetylenes. 

The pyrazole analogues of anthranilic acids or anthranilonitriles are a convenient source of [5.6] fused systems (for a general review see (80T2359)). Thus 5-amino-4-cyanopyrazoles (in some examples an ester or a hydrazido group replaced the cyano group) have been transformed into pyrazolo[3,4-d]pyrimidines (552) and into pyrazolo[2,3-e]diazepinones (553), and 4-amino-5-methoxycarbonylpyrazoles have been converted into pyrazolo[4,3-d]pyrimidines (554). 

Figure 4.2. Rotational-energy barriers as a function of substitution. Tbe small barrier ( 2kcal) in ethane (a) is lowered even further ( O.Skcal) if three bonds are tied back by replacing three hydrogen atoms of a methyl group by a triple-bonded carbon, as in methylacetylene (b). The barrier is raised 4.2 kcal) when methyl groups replace the smaller hydrogen atoms, as in neopentane (c). Dipole forces raise the barrier further ( 15 kcal) in methylsuccinic acid (d) (cf. Figure 4.3). Steric hindrance is responsible for the high barrier (> 15 kcal) in the diphenyl derivative (e). (After...

Diphenylthioalkanes react with mercuric fluoride to give 1-fluoro-l-phenylthio-alkanes. Provide a detailed description of a likely mechanism for this reaction. Consider such questions as (1) Is an SnI or an Sn2 process most likely to be involved (2) Would NaF cause the same reaction to occur (3) Why is only one of the phenylthio groups replaced ... 

When an organofunctional group replaces a methyl group on a siloxy unit, a superscript is used to describe the unit. The most common groups that are encountered can be symbolized as alkyl (R), hydrogen (H), phenyl (Ph), hydroxyl (OH), trifluoropropyl (F), and vinyl (Vi). Thus, vinyl-endblocked-PDMS is represented by (Scheme 3), and a trimethylsiloxy-... 

Corypalline, CnHijOjN (Corydalis spp. Nos. 9, 22 list, p. 170). This phenolic base, m.p. 168°, picrate, m.p. 178°, contains one methoxyl group and on methylation yields 2-methyl-6 7-dimethoxytetrahydrof5oquinoline, Ci2Hi,02N, m.p. 82°, and on ethylation, 2-methyl-6-methoxy-7-ethoxy-tetrahydrofsoquinoline, m.p. 65°, whence the free hydroxyl appears to be at C and this has been confirmed by the synthesis of corypalline by a method analogous with that used by Spath, Orekhov and Kuffner. Corypalline is therefore hydrohydrastinine (XII) with the methylenedioxy group replaced by MeO at C and. OH at C (Manske). ... 

To dehydrolaudanosoline chloride Robinson and Sugasawa, and independently Schopf and Thierfelder ascribe formula (VI), which makes it 2 3 11 12-tetrahydroxy-8-methyldibenzotetrahydropyrrocolinium chloride. The primary tetracetyl-derivative, m.p. 148°, is represented by (VII R = acetyl) and the second acetyl derivative, m.p. 215°, by (VII R = acetyl) with an ethylenic linkage between carbon atoms 15 and 16. Similarly, the initial tetramethoxy-derivative is to be represented by (VI) with the four hydroxyl groups replaced by methoxyl groups the primary product formed on heating, by loss of methyl chloride, will be represented by (VII R = OMe), and the second product, m.p. 201-3°, of the reaction will be represented by (VII R = OMe), with an ethylenic linkage between and C e-... 

Bicuculline, C2oHi,06N. (Items 1, 9, 10, 13, 14, 18, 20, 23-26, 34, 35, 38 list, p. 169). This alkaloid exists in two forms, m.p. 177° and m.p. 196°, and has [a], ° + 130- 5° (CHCI3). The hydrochloride has m.p. 259° (dec.) and from the methiodide, W-methylbicuculline, plates, m.p. 246°, has been prepared. Bicuculline contains no methoxyl groups it behaves as a lactone and is convertible by alkalis into bicucine, which is possibly the corresponding hydroxy-aeid (see below). It simulates hydrastine in its reactions and differs from that base by CH, indicating that a methylene-dioxy group replaces two methoxyl groups, and this view is supported by comparison of the products of oxidative hydrolysis of the two alkaloids. Both yield hydrastinine (p. 163) as the basic product, but while hydrastine provides as the second product, opianic acid,... 

Cordrastinc, Ci8Hi302N(0Me)4. (Item 9 list, p. 170). Colourless needles, m.p. 196°. Its composition and reactions suggest that it belongs to the phthalideisoquinoline group and is represented by formula (I) (with R = H and the two dioxymethylene groups replaced by four methoxyl groups). ... 

A few groups replace the Lennard-Jones interactions by interactions of a different form, mostly ones with a much shorter interaction range [144,146]. Since most of the computation time in an off-lattice simulation is usually spent on the evaluation of interaction energies, such a measure can speed up the algorithm considerably. For example, Viduna et al. use a potential in which the interaction range can be tuned... 

Alkylthio groups replace the fluorine atoms of pentafluorobenzene derivatives tvith relative ease, but selectivity is difficult to eontrol [27] (equation 17). 

Nitrosodimethylaniline.—It is a peculiarity of the tertiary aromatic amines, which distinguish them fiom the corresponding aliphatic compounds, that they arc capable of reacting with nitrous acid. Here the nitroso-group replaces hydrogen in the para-position to the dimethylamino-group. 

An ATP analog, /3, y-methylene-ATP, in which a —CHg— group replaces the oxygen atom between the /3- and y-phosphorns atoms, is a potent inhibitor of muscle contraction. At which step in the contraction cycle would you expect /3, y-methylene-ATP to block contraction ... 

If a methyl group replaces a hydrogen atom on the carbon of the C==N bond across which addition of water occurs, a considerable reduction in the extent of water addition is observed. Conversely, the existence of such a blocking effect can be used as a provisional indication of the site at which addition of water occurs, while the spectrum and acid dissociation constant of the methyl derivative provide a useful indication of the corresponding properties of the anhydrous parent substance. Examples of the effect of such a methyl group on equilibria are given in Table IV. 

---