Hydrocarbon framework branched

When you draw diagrams like these to indicate the three-dimensional shape of the molecule, try to keep the hydrocarbon framework in the plane of the paper and allow functional groups and other branches to project forwards out of the paper or backwards into it,... 

Hydrocarbon frameworks rarely consist of single rings or chains, but are often branched. Rings, chains, and branches are all combined in structures like that of the marine toxin palytoxin that we met at the beginning of the chapter, polystyrene, a polymer made of six-membered rings dangling from linear carbon chains, or of p-carotene, the compound that makes carrots orange,... 

These rules work for hydrocarbon frameworks that are chains or rings, but many skeletons are branched. We can name these by treating the branch as though it were a functional group ... 

Hydrocarbons also differ from one another in the way the carbon atoms connect to each other. Figure 12.1 shows the three hydrocarbons n-pentane, wo-pentane, and neo-pentane. These hydrocarbons all have the same molecular formula, CSH]2, but are structurally different from one another. The carbon framework of n-pentane is a chain of five carbon atoms. In zro-pentane, the carbon chain branches, so that the framework is a/o r-carbon chain branched at the second carbon. In neo-pentane, a central carbon atom is bonded to four surrounding carbon atoms. 

The preparation of other branched triangulanes with varying symmetries has also been reported. A notable feature of this series of small hydrocarbon cascades is that the framework is composed entirely of quaternary, tetraalkyl-substituted carbons. This unique architecture closely resembles or is at least reminiscent of Maciejewski s 16 proposed cascade molecule comprised of an all 1 — 3 C-branched interior framework (i.e., without spacers between branching centers). 

Draw good diagrams of saturated hydrocarbons with seven carbon atoms having (a) linear, (b) branched, and (c) cyclic frameworks. Draw molecules based on each framework having both ketone and carboxylic acid functional groups. 

For skeletal rearrangements over zeolite, the nonclassical protonated cyclopropane intermediate could account for the experimental observations. Theoretical studies of the reaction mechanism indicated that protonated cyclopropane-type species do not appear as intermediates but rather as transition states. Considering all zeolite-catalyzed hydrocarbon reactions (hydride transfer, alkylation, disproportionation, dehydrogenation), only carbocations in which the positive charge is delocalized or sterically inaccessible to framework oxygens can exist as free reaction intermediates. In theoretical studies on the mechanism of the superacid-catalyzed isomerization of n-alkanes (ab initio and DFT calculations), protonated cyclopropanes were found to be transition states for the branching of both the 2-butyl cation and the 2-pentyl cation. ... 

Configurationally biased Monte Carlo techniques [63-65] have made it possible to compute adsorption isotherms for linear and branched hydrocarbons in the micropores of a siliceous zeolite framework. Apart from Monte Carlo techniques, docking techniques [69] have also been implemented in some available computer codes. Docking techniques are convenient techniques that determine, by simulated annealing and subsequent freezing techniques, local energy minima of adsorbed molecules based on Lennard-Jones-or Buckingham-type interaction potentials. 

It is this possibility for variation of the pore size that leads to an important property of zeolites, that of molecular sieving. A zeolite is able to accommodate or reject molecules based on their size. Using suitable drying methods, the water within a zeolite framework can be removed the resulting dehydrated zeolite has space to accommodate other small molecules. So, if we have a mixture containing some molecules of suitable size and shape to enter the pores of the zeolite, and other molecules that are not able to do so, an effective separation can be carried out. A mixture of straight-chain and branched-chain hydrocarbons is one such example. 

Molecular-sieving effects based on size/shape exclusion are common in rigid zeolites and molecular sieves. One famous example is the separation of normal paraffins from branched-chain and cyclic hydrocarbons by using a 5-A molecular sieve. Similar selective adsorption effects have been observed in several porous MOFs. Kim and coworkers reported that Mn(HCOO)2 has a robust 3D framework structure with ID channels interconnected by small win-do ws/apertures. This material can selectively adsorb H2 over N2 and Ar at 78 K, and CO2 over CH4 at 195 K, as indicated by the gas adsorption isotherms. In both cases, the uptake of the excluded gases N2, Ar, and CH4 was negligible. Thus, the selectivity was attributed to the small aperture of the channels. An interpenetrated MOF, PCN-17, contains nanoscopic cages with a window size of 3.5A and displays selective adsorption of H2 and O2 over N2 and CO. ° MIL-96 " and Zn2(cnc)2(dpt) were also found to selectively adsorb CO2 over CH4 based on size/shape... 

D channel of the framework is composed of oval-shaped cages of diameter 5.1 A, connected by small necks with a diameter of 3.2 A each of the cages is 7.3 A in length along the channel. Such pore characteristics offer unique adsorption behavior for the framework, with exclusion of all branched hydrocarbons and any paraffin or olefins longer than C4. The cage effect leads to commensurate adsorption for smaller molecules such as propane and... 

Hydrocarbons are oxidized without the introduction of a radical source but this oxidation occurs with autoacceleration. This autoacceleration was explained in the framework of the theory of degenerate-branched chain reactions by the formation of an intermediate product, initiator. It was proved in 1930-50 that these products are hydroperoxides (see above). The Bach-Engler peroxide theory was thus merged with Semenov s theory of degenerate branching. Soviet scientists made the decisive contribution to the development of this area. 

Aliphatic framework molecules most common in organic acids include alkanes (saturated hydrocarbons) and alkenes (unsaturated hydrocarbons). These saturated and unsaturated aliphatic carboxylic acids may be acyclic (straight or branched chains) or alicyclic (aliphatic rings). Acyclic aliphatic monocarboxylic acids are also referred to as fatty acids (Table 1). The first five saturated acids (formic to valeric) of this type are sometimes referred to as short-chain, low-molecular-weight, or volatile fatty acids. Although a nomenclature for these acids has been established by the International Union of Pure and Applied Chemistry (lUPAC), the convention of using the trivial names for the first five saturated acids has remained. Similarly, trivial names are used for the aliphatic dicarboxylic acids (Table 2) that are saturated with two to four carbon atoms (C2-C4) and unsaturated with four carbon atoms (C4). Alicyclic carboxylic acids contain one or more saturated or partially unsaturated rings. These acids most commonly occur... 

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