Naphthenic rings

Or by a naphthenic ring which can also be substituted for two adjacent hydrogen atoms forming a naphthene aromatic such as tetralin or tetra.hydronaphthaiLene. ... 

Structurally the difference between PEN and PET is in the double (naphthenic) ring of the former compared to the single (benzene) ring of the latter. This leads to a stiffer chain so that both and are higher for PEN than for PET (Tg is 124°C for PEN, 75°C for PET is 270-273°C for PEN and 256-265°C for PET). Although PEN crystallises at a slower rate than PET, crystallization is (as with PET) enhanced by biaxial orientation and the barrier properties are much superior to PET with up to a fivefold enhancement in some cases. (As with many crystalline polymers the maximum rate of crystallisation occurs at temperatures about midway between Tg and in the case of both PEN and PET). At the present time PEN is significantly more expensive than PET partly due to the economies of scale and partly due to the fact that the transesterification route used with PEN is inherently more expensive than the direct acid routes now used with PET. This has led to the availability of copolymers and of blends which have intermediate properties. 

The n-d-M correlation is an ASTM (D-3238) method that uses refractive index (n), density (d), average molecular weight (MW), and sulfur (S) to estimate the percentage of total carbon distribution in the aromatic ring structure (% C ), naphthenic ring structure (Cj,), and paraffin chains (% Cp). Both refractive index and density are either measured or estimated at 20°C (68°F). Appendix 4 shows formulas used to calculate carbon distribution. Note that the n-d-M method calculates, for example, the percent of carbon in the aromatic ring... 

These observations can be explained taking into consideration that in this study the metal particle sizes were relatively large in all three catalysts, so the dicarbene mechanism dominated, even on the Pt-based catalysts. In any case, a somewhat higher selectivity towards substituted C-C cleavage was observed on the Pt catalysts, relative to the monometallic Ir catalyst. However, as we have recently pointed out, unless the naphthenic rings are opened very selectively at the substituted C-C bonds, no considerable gain in CN can be achieved by RO. This was not the case in any of the Pt-Ir catalysts presented in ref. 111. 

Side chains are broken free of ring structure dehydrogenation of naphthenic rings containing nine or more carbon atoms is common... 

Paraffin conversion to naphthenes is very unfavorable (last column of Table IV). For paraffins to be converted to naphthenes by ring closure, naphthenes must be at very low concentrations. If appreciable naphthenes exist, such as at short catalyst contact times, naphthene ring opening to paraffins can occur. Again, equilibria improve with carbon number. Eight-and nine-carbon paraffins behave quite similarly. 

Cracking involves aromatic dealkylation and cracking of paraffins, methylene linkages, and naphthenic rings. Aromatic dealkylation is rather easy under current liquefaction conditions (below 450°C) however, the cracking reactions are not facile. Competitive reactions of various species should be carefully considered in catalyst design. 

The carboxylic acid group usually is attached to a naphthenic ring rather than an aromatic ring. These organic acids generally are known by the rather loose term naphthenic acids. These acids may be neutralized with common bases. For instance, the acid number of a crude oil is the number of milligrams of potassium hydroxide required to neutralize the... 

Terms such as paraffinic, naphthenic, naphthenic-aromatic, and aromatic-asphaltic are used in the several classification methods which have been proposed. These terms obviously relate to the molecular structure of the chemical species most prominent in the crude oil mixture. However, such classification is made difficult because the large molecules usually consist of condensed aromatic and naphthenic rings with paraffinic side chains. The characteristic properties of the molecules depend on the proportions of these structures. 

The decomposition of the alkoxy radical by Reaction 8 occurs by a-scission at the C—C bond attached to the largest hydrocarbon group (185, 229). Straight-chain paraffins produce aldehydes, while highly branched paraffins yield ketones (Reaction 11). The knock resistance of naphthenes may be caused by the stability of the naphthene ring to C—C scission (25). 

Since rc and rh can be considered as constants for the majority of the hydrocarbons present in saturated natural mineral oils (the influence of the presence of naphthenic rings, of branches, and of cis-trans isomers can be neglected in a first approximation), it follows from equation (12) that there is a linear relationship between and %H. 

Thus it is possible to calculate the number of naphthenic rings of saturated oil fractions from the specific refraction and molecular weight by means of equation (15). The number of rings can also be determined from Fig. 4, in which the relationship between r c, M and Rn (besides that between %H, M and Rn) has been constructed by means of equation (15), which has been transformed into... 

With these diagrams it is possible to find the number of (naphthenic) rings per molecule from the molecular weight and kinematic viscosity. However, the accuracy of this determination is in some regions rather small. This is one of the reasons why another diagram13 14 has been introduced, in which vf0 has been plotted against the refractive index Fig. 13. Another reason is that the molecular weight is preferably... 

The naphthenic ring is thus considered as a form of branching that contributes three times as much as a side chain. 

Thus the contributions of these compounds to the specific refraction r of the fractions cancel out [cf. eqn. (71)] this is the reason that diagrams for the ring analysis of saturated mineral oil fractions based on specific refraction and molecular weight are also valid for the estimation of naphthenic rings in aromatic fractions cf. p. 24). 

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