Isomers of hydrocarbons

Isomers of hydrocarbons are produced by differences in the position of carbon atoms or of multiple bonds or both, chemskiii Builder 24.1 Numbering of carbon chains starting at both ends is done for single... 

In oil processing, separation of aromatic isomers Cg (ethylbenzene 7b= 136°C,p-xylene 7b= 138.3°C, m-xylene Ty, = 139.1°C, >-xylene T], = 144.4°C) is required. According to the literary data, the following isomers of hydrocarbons are separated p-xylene/m-xylene, p-xylene/o-xylene, -hexane/2,2-dimethylbutane, -hexane/3-methylpentane, and n-butane/f-butane [8,83,130-137]. Pervaporation method is the most effective for this purpose. To separate the isomers, membranes based on various polymers were used. Good separation for aU isomer mixtures was attained by the polyimide Kapton film (fip = 1.43-2.18) but parylene films and cellulose acetate also exhibited a relatively high separation factor (fip = 1.22-1.56 and /3p = 1.23-1.56, respectively). Temperatures >200°C were required to obtain a reasonable flux through the polyimide film and a pressure of about 20 atm was necessary to keep the feed stream liquid [8]. 

The Naming of Cis and Trans Isomers of Hydrocarbons Containing Olefin Double Bonds. A committee report. No charge. 

Branched-chain isomers Structural isomers of hydrocarbons that have carbon-carbon bonds in side chains... 

Isomers of hydrocarbons will be characterized by slightly different boiling points whereas an ethyl alcohol and dimethyl ether (which are isomers) have very different physical and chemical properties, a. Aldehyde... 

It has been recently shown, however, that the infrared intensities of rotational isomers of hydrocarbons cannot be very satisfactorily reproduced with the set of eop s derived from all trans molecules. One is then faced with the problem of the determina-tions of the electrical interactions between adjacent bonds in gauche and trans positions. This problem is presently being analyzed in our laboratory. 

A major challenge is how to handle the large number of isomers of hydrocarbons that are possible in lubricant range materials. These range from a billion at C30 to a billion billion at C50. Few of these have relevance as lubricants and judicious selection of representative isomers and groups of isomers is needed. Experimental validation of computed results is also problematic since there are few pure isomers available in this range. Nevertheless, the simulations done so far have been very helpful in guiding synthesis. 

The idea of representing a bond by means of a straight line joining the atomic symbols, we probably owe to Alexander Crum Brown. Prankland, with due acknowledgement, adopted Crum Brown s representation which put circles round the atom symbols but by 1867 the circles had been dropped, and more-or-less modern chemical notation became widespread. This was, in some measme, almost certainly because of the ease with which isomers of hydrocarbons could be represented and enumerated within this approach as shown especially in the work of Cayley [Cayley, 1874]. The graphical notation and the ideas of Prankland were further developed by Werner in the 1890s in his coordination theory for inorganic complexes. 

Although isomerization processes have developed slowly because of the cost of handling corrosive catalytic agents and the cost of separating the isomers of hydrocarbons that contain five or more carbon atoms, the increasing need for high-octane-number fuels will require a more extensive use of isomerization processes. Branched-chain compounds have much... 

Exclusive of compounds with double bonds four hydrocarbons are constitutional isomers of cis and trans 1 2 dimethylcyclopropane Identify these compounds... 

Selenourea [630-10-4] ]5k.e urea and thiomea can form channel inclusion compounds (87) with a variety of hydrocarbons. Though the difference in channel diameter between thiourea and selenourea is small, selenourea seems to be much more selective for the inclusion of certain guest molecules (eg, cis/trans isomers). 

Cyclodienes. These are polychlorinated cycHc hydrocarbons with endomethylene-bridged stmctures, prepared by the Diels-Alder diene reaction. The development of these insecticides resulted from the discovery in 1945 of chlordane, the chlorinated adduct of hexachlorocyclopentadiene and cyclopentadiene (qv). The addition of two Cl atoms across the double bond of the ftve-membered ring forms the two isomers of chlordane [12789-03-6] or l,2,4,5,6,7,8,8-octachloro-2,3,3t ,4,7,7t -hexahydro-4,7-methano-lJT-indene, QL-trans (mp 106.5°C) and pt-tis (32) (mp 104.5°C). The p-isomerhas signiftcantiy greater insecticidal activity. Technical chlordane is an amber Hquid (bp 175°C/267 Pa, vp 1.3 mPa at 25°C) which is soluble in water to about 9 fig/L. It has rat LD qS of 335, 430 (oral) and 840, 690 (dermal) mg/kg. Technical chlordane contains about 60% of the isomers and 10—20% of heptachlor. It has been used extensively as a soil insecticide for termite control and as a household insecticide. 

Within each analogous series of hydrocarbons there exist isomers of the compounds within that series. An isomer is defined as a compound with the same molecular formula as another compound but with a different structural formula. In other words, if there is a different way in which the carbon atoms can align themselves in the molecule, a different compound with different properties will exist. 

As in the alkanes, it is possible for carbon atoms to align themselves in different orders to form isomers. Not only is it possible for the carbon atoms to form branches which produce isomers, but it is also possible for the double bond to be situated between different carbon atoms in different compounds. This different position of the double bond also results in different structural formulas, which, of course, are isomers. Just as in the alkanes, isomers of the alkenes have different properties. The unsaturated hydrocarbons and their derivatives are more active chemically than the saturated hydrocarbons and their derivatives. 

Perfluocoalkyl groups thermodynamically destabilize double bonds and small rings, but they can kineiically stabilize highly stramed molecules [75]. This remarkable perfluoroalkyl effect has made possible the isolation of stmctures that are uncommon m hydrocarbon chemistry, especially valence-bond isomers of aromatics and heteroaromatics such as 1, 2, and 3 [108],... 

Figure 14.1 The number of possible hydrocarbon isomers of fractions with up to 20 carbon...

When the terpene a-fenchene (isopinene) is hydrated by means of acetic and sulphuric acids, it yields an isomer of fenchyl alcohol, which is known as isofenchyl alcohol (q.v.), and which on oxidation yields iso-fenchone, as fenchyl alcohol yields fenchone. The two ketones, fenchone and isofenchone, are sharply differentiated by isofenchone yielding iso-fenchocamphoric acid, Cj Hj O, on oxidation with potassium permanganate, which is not the case with fenchone. According to Aschan,i the hydrocarbon found in turpentine oil, and known as /9-pinolene (or cyclo-fenchene—as he now proposes to name it), when hydrated in the usual manner, yields both fenchyl and isofenchyl alcohols, which on oxidation yield the ketones fenchone and isofenchone. According to Aschan the relationships of these bodies are expressed by the following formulae —... 

Azulene, a beautiful blue hydrocarbon, is an isomer of naphthalene. Is azulene aromatic Draw a second resonance form of azulene in addition to that shown. 

Azulene, an isomer of naphthalene, lias a remarkably large dipole moment for a hydrocarbon (/i = 1.0 D). Explain, using resonance structures. 

Although the —CH2— group could be inserted in other places, the free rotation about single C—C bonds in hydrocarbons allows the resulting molecules to be twisted into one or the other of these two isomers. Both compounds are gases, but butane (24) condenses at —1CC, whereas methylpropane (25) condenses at — 12°C. Two molecules that differ only by rotation about one or more bonds may look different on paper, but they are not isomers of each other they are different conformations of the same molecule. Example 18.3 illustrates how to tell if two molecules are different isomers or different conformations of the same isomer. 

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