Phenyl ring

First, it is possible to excite a chromophore corresponding to the active site, and detennine which modes interact with it. Second, by using UV excitation, the amino acids with phenyl rings (tryptophan and tyrosine, and a small contribution from phenylalanine) can be selectively excited [4], The frequency shifts in the resonance Raman spectrum associated with them provide infomiation on their enviromnent. 

As an example, the empirical formula of phenylalanine may be split into a more extended form that shows the presence of a phenyl ring, as well as an amino and a carboxylic acid group (the condensed form in Figure 2-4). 

As can be seen, this algorithm additionally identifies constitutionally equivalent atoms. These are atoms with the same EC value (3) in the final iteration, such as the two carbon atoms in the ortho positions of the phenyl ring with an EC value of 9 (Figure 2-44). 

Example Anoth er example of Iron tier orbital theory uses the reaction ol phenyl-butadiene with ph en ylethylene. This reaction is a [4-1-21 pericyclic addition to form a six-membered ring. It could proceed with the two phenyl rings close to each other (head to head) or further away front each other (head to tail). 

A con jugated sp - -sp --" single bond (for example, the bond joining the tw o phenyl rings of biphenyl, the central bond of butadiene, with delocali/ed aromatic bonds, or phenyl amine, where N-G bond is labeled aromatic and nitrogen is sp2 b h ybridi/ed) IS described by a two-fold barrier, V2=l() kcal/mol. 

Tabus VI. Akomatic (Phenyl) Ring Absorption Frequencies ... 

Band 5, 6-25y. (1601 cm. i). Aromatic (phenyl) ring absorption. The weak shoulder at 6-33p. (1580 cm. i) may be noted. When the aromatic ring is conjugated, as in the present example, the aromatic (phenyl) band is often split into a doublet and is usually more pronounced (Table III). 

The nitration of nitro- and dinitro-biphenyls has been examined by several workers. i - As would be expected, nitration of the nitro-biphenyls occurs in the phenyl ring. Like a phenyl group, a nitrophenyl group is 0 -directing, but like certain substituents of the type CH CHA ( 9.1.6) it is, except in the case of w-nitrophenyl, deactivating. Partial rate factors for the nitration at o °C of biphenyl and the nitro-biphenyls with solutions prepared from nitric acid and acetic anhydride are given below. The high o p-v2X o found for nitration of biphenyl... 

The nitration of phenylpyridines and related compounds has attracted attention for a long time, and measurements of isomer proportions have been made for several compounds of this type. Nitration occurs in the phenyl ring. For 2-phenylpyridine and 2-phenylpyridine i-oxide measurements of the dependence of rate of nitration upon acidity in 75-81 % sulphuric acid at 25 °C show that both compounds are nitrated as their cations (table 8.1). The isomer distribution did not depend significantly upon the acidity, and by comparison with the kinetic data for quinolinium ( 10.4.2) the partial rate factors illustrated below were obtained.They should be compared with those for the nitration of 2-nitrobiphenyl ( 10.1). The protonated heterocyclic groups are much... 

But that is not the case. What the Korean lab found out was that when this procedure is performed, the OH stabilizes on the alpha carbon. That is the carbon right next to the phenyl ring. If one has any use for it as is then that is fine. But what is most preferable is to reduce the OH to get the propenylbenzene (say isoelemicin for our example). Using the simple potassium bisulfate reduction recipe, one can get rid of the OH with no problems at all. 

The crystal and molecular structures of 2-amino-4-phenylthiazole hydrobromide have been determined by radiocrystallography the angle between the thiazole and phenyl rings was found to be 19 . The major features are reported in Fig. VI-4 (142). 

Acetamidothiazole is nitrated in the same way (58, 378, 379). 2-Acetamido-4-phenylthiazole is reported to be nitrated on C-5 (380) as opposed to 2-amino-4-phenylthiazole, where nitration occurs on the phenyl ring (381). This latter result is not consistent with the other data on electrophilic reactivity in most cases 2-amino-4-arylthiazole derivatives react with electrophilic reagents at the C-5 position (see Sections rV.l.B and D). Furthermore, N-pyridy]-(2)-thiazolyl-2-amine (178) is exclusively nitrated on the thiazole ring (Scheme 113) (132, 382). 

Anilino-4-arylthiazoles (211) are mercurated on the phenyl ring (Scheme 133) (453. 454). The phenyl ring is also the site of mercuration in 2-arylamino-4-(2-thienyl)thiazoles (213) (Scheme 134) (455). 

The preparation of 5-azothiazoles uses the nucleophilic character of C-5 carbon in reaction with the appropriate diazonium salt (402, 586). These 5-azothia2oles form 1 1 complexes with Ag (587). 2-Amino-4-methyl-5-arylazothiazoles give reduction waves involving two-electron transfer the Ej/ values correlate to the angle between the thiazole and phenyl rings (588). 

As in the case of thiazole and the alkylthiazoles, cleavage of the thiazole ring takes place at the 1,2 and 3,4 bonds, confirmed by a metastable peak. The other important peaks result from fragmentation of thiirenium ion, in the case of 4- and 5-phenylthiazole and of the phenyl ring. These latter are generally present in the spectra of all comptmnds with benzene-ring substituents, they occur at m/e 77, 76, 75, 51, 50, 39 (124). The ion m/e 45 (HCS" ) is always present. 

For nonsubstituted phenyl thiazoles or for alkylarylthiazoles, one of the problems investigated is the determination of the angle between the aryl and the thiazole rings. In the case of 4,5-diphenylthiazole the problem is complicated by the interaction of the two phenyl rings (126). 

In acetic acid, mercuration occurs at the 5-position at room temperature. At 60 to 70°C in the case of arylthiazoles, where the 5-position is unsubstituted, mercuration also takes place at the para-position of the phenyl ring (861). 

Axylthiazoles undergo electrophilic substitution mainly in the para-position of the phenyl ring. In some cases, it is also possible to substitute the 5-position of the thiazole nucleus (244-246). 

Arylthiazoles are nitrated on the phenyl ring. The yields in sulfuric acid average 60 to 85% (248). Results are indicated in Table III-46 (250). 

For 2-R-substituted 4-phenylthiazoles, the influence of R groups on the yield of substitution has been reported (see Table III-47). Substitution occurred at the para-position of the phenyl ring (249). 

Increment (in nm) for each substituent on phenyl ring —Alkyl or ring residue ... 

F)-3[l-(2,5-dimethyl-3-furanyl)ethyHdene](-4-isopropyHdene-2,5furandione [59000-86-1/, where Rj = R2 = R3 = and the phenyl ring is... 

The birefringence for phenyl-substituted PC (4) (T = 176 C) is reduced to about 50%, for benzyl substituted PC (5) (T = 138 C) to about 25%, and for four-ring bisphenol PC (6) to 8% of the value for BPA-PC (183,190,195,197,198) on condition of an optimum conformation of the phenyls in the side groups perpendicular to the aromatic rings in the backbone. In reaUty, however, these low birefringence values are not achieved, because the optimum conformation of the phenyl rings cannot be achieved in injection-stamped disks. 

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