Pentane, molecular model

Recent conformational calculations made on the 2,4-bis(2-naphthyl)-pentanes 1371 gave results similar to the diphenylpentanes. The tt state (EFS) in the 2-naphthyl meso isomer was found to be 2.3 kcal/mole higher than the tg, g+t state, consistent with a larger repulsion between naphthyl rings than for phenyl rings. It is apparent from molecular models, and has been confirmed by Seki et al.138,139), that the... 

Procedure Construct the model of one C5II ]2 molecule and position it on one side of the table together with models of 02 molecules on the other side of the table, place models of C02 and H20 molecules. Ask how many molecule models are on both sides of the table 5C02 molecules can be formed from 5 C atoms in one pentane molecule 6 H20 molecules can be formed from 12 H atoms in one pentane molecule. Finally, a counts of 8 02 molecular models are needed. 

As we learn about physical chemistry, we extend that understanding to new systems of interest, but the transition from simple molecules to more complicated systems is limited by our human abilities. We can imagine a butane molecule and imagine both how and why different conformers are preferred. When we tackle pentane or combinations of functional groups, however, it becomes difficult to simultaneously consider the relative effects of electrostatics, steric interactions, and bulk properties, such as solubilities. Fortunately, we can construct models in software that allow us to properly treat all of these interactions. The scientific field of molecular modeling or. more generally, computational chemistry is the practice of simulation of molecular systems with sufficient detail to address a question of interest. 

Draw the structures of the three isomers of pentane. It may help to make models of the isomers. If you do not have a molecular modelling kit, use straws to represent bonds and plasticine balls, of different colouts, to represent atoms of hydrogen and carbon. 

Rank the groups attached to each stereogenic center. Identify each stereogenic center as either R or S according to the methods described in Chapter 7. Remember that the proper orientation of the lowest ranked group (usually H) is away from you. Molecular models will be helpful here. Each of the stereogenic centers in D-ribose has the R configuration. The lUPAC name of D-ribose is (2R,3R,4R)-2,3,4,5 -tetrahy droxy pentanal. 

The simplest spiro alkane is spiro[2.2]pentane, a molecular model of which illustrates an interesting structural feature of spiro compounds. The two rings lie at right angles to each other. 

Compare -pentane in the GG state with isotactic PP in an all-trans conformation. Build the molecules using a molecular model and make the comparison. 

Maleate/vinyl ether formulations based on a model unsaturated polyester prepared from maleic anhydride and 1,5-pentane diol and triethylene glycol divinyl ether were studied. At molecular weights of less than about 10,000 the cured films were extremely brittle. When the equivalent weight of the unsaturated polyester was increased by replacing some of the maleic anhydride with succinic anhydride, measurable values for film elongation could be obtained but the cure speed was definitely slower. When either diethyl maleate or isobutyl vinyl ether were added as monofunctional diluents the cure dose needed to obtain 200 MEKDR was increased and the flexibility measured by pencil hardness increased as the amount of diluent was increased. A urethane vinyl ether was synthesized and used to replace DVE-3 and films with increased elongation were obtained at equivalent at dosages as low as 1 J/cm2. 

A very common approximation goes by the name of rotational isomeric state model (RIS). With such a model it is assumed that the molecular population is placed exclusively in a few energy minima, always according to the Boltzmann distribution. The conformations corresponding to the minima are called conformers, or rotational isomers, and are indicated by one or more letters (G, T) for butane three conformers are considered (G, T, G ), for pentane five (TT, G T, TG, G G, G G ). A more detailed examination of pentane reveals the existence of two further wells (fl, = 65 , 2 = 260° and 0, = 100°, 02 = 295°), sometimes indicated by G G and G G , respectively, close to the forbidden G G" conformation, but with a much tower energy (157, 158). 

The photo-oxidation of n-butane has been modelled by ab initio and DFT computational methods, in which the key role of 1- and 2-butoxyl radicals was confirmed.52 These radicals, formed from the reaction of the corresponding butyl radicals with molecular oxygen, account for the formation of the major oxidation products including hydrocarbons, peroxides, aldehydes, and peroxyaldehydes. The differing behaviour of n-pentane and cyclopentane towards autoignition at 873 K has been found to depend on the relative concentrations of resonance-stabilized radicals in the reaction medium.53 The manganese-mediated oxidation of dihydroanthracene to anthracene has been reported via hydrogen atom abstraction.54 The oxidation reactions of hydrocarbon radicals and their OH adducts are reported.55... 

All three have five carbon atoms and 12 hydrogen atoms, so they have the molecular formula C5H12. However, as you can see, these models represent three different arrangements of atoms, pentane, 2-methylbutane, and 2,2-dimethylpropane. These three compounds are isomers. Isomers are two or more compounds that have the same molecular formula but different molecular structures. Note that cyclopentane and pentane are not isomers because cyclopentane s molecular formula is C5H10. 

In order to make this process more understandable, the molecular building set can be used (see E10.10) the structure model of a pentane molecule, C5H12, should be constructed and also the isomers, the reaction of pentane with oxygen can be modeled practically or mentally by the use of 02 molecules models. The students should learn that a maximum of 5 C02 molecules and 6 H20 molecules can result from one C5H12 molecule. The reaction equation can only be properly understood after carrying out this reflection on the amount of related molecules ... 

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