2.2- Dimethylpropane structure

When the objective is analytical the products of ozonolysis are isolated and identi lied thereby allowing the structure of the alkene to be deduced In one such example an alkene having the molecular formula C Hig was obtained from a chemical reaction and was then subjected to ozonolysis giving acetone and 2 2 dimethylpropanal as the products... 

Figure 12.3 Mass spectrum of 2,2-dimethylpropane (C5Hi2 MW = 72). No molecular ion is observed when electron-impact ionization is used. (What do you think is the structure of the M+ peak at m/z = 57 )...

Dispersion forces increase in strength with the number of electrons, because larger electron clouds are more polarizable than smaller electron clouds. For molecules with comparable numbers of electrons, the shape of the molecule makes an important secondary contribution to the magnitude of dispersion forces. For example. Figure 11-11 shows the shapes of pentane and 2,2-dimethylpropane. Both of these molecules have the formula C5 H12, with 72 total electrons. Notice that 2,2-dimethylpropane has a more compact structure than pentane. This compactness results in a less polarizable electron cloud and smaller dispersion forces. Accordingly, pentane has a boiling point of 36 °C, while 2,2-dimethylpropane boils at 10 °C. 

Fig. 10.7. Computational (B3LYP/6-31G(d)) minimum-energy structure of carbomethoxycarbene derivative of copper N,N -dimethylpropane-l,3-diimine. Reproduced from J. Am. Chem. Soc., 123, 7616 (2001), by permission of the American Chemical Society.

Heterocyclic nitrogen donors and their adducts with zinc chloride have been studied.623,624 A large number of other ligand systems have also been characterized, for example, zinc halide adducts of 2,2-dimethylpropane-1,3-diamine and hexamethylphosphoramide have been studied.625,626 The formation of mixed ligand complexes with chloride and substituted pyridines has been studied.627 The zinc tris(pyridyl) chloride anion has also been structurally characterized.628 Manganese(II) ions have been used to probe the stereochemistry in reactions of zinc halides with pyrazine.629... 

Problem 4.32 Give topological structural formulas for (a) propane, (h) butane, (c) isobutane, (d) 2,2-dimethylpropane, (e) 2,3-dimethylbutane, (/), 3-ethylpentane, (g) l-chloro-3-methylbutane, (h) 2,3-dichloro-2-methylpentane, (/) 2-chloro-2,4,4-trimethylpentane. -4... 

We now extend the structural basis set for cobalt(III) hexaamines with one additional structure with relatively long Coin-N bonds. The [Co(tmen)3]3+ cation (tmen = 2,3-dimethylpropane-2,3-diamine) is a highly strained species with long Com-N bonds because of the four methyl substituents (see Fig. 17.12.1). The structure of the cation has been determined by an X-ray diffraction study, and the conformation in the crystal has been defined as 065 (see Section 17.3 for the nomenclature of the conformers). Due to the elongation of the Com-N bonds to 1.997 A, there is a remarkable shift in the ligand field spectra (the first d-d transition ( Ai- ) is at 515 nm vs 470 nm for [Co(en)3p ) and the redox potential (-0.18 V vs +0.28 V)[56>231]. 

Dimethylpropane (neo-pentane) is unique amongst the isomers of pentane since it contains no secondary or tertiary C—H bonds. This unusual structure of the dimethylpropyl radical has been exploited in the study of... 

In the same way, CH3-CHZ-CH2-CH2-CH3 is pentane CH3-CH2-CH(CH3)-CH3 is 2-methylbutane and not 3-methyIbutane as this makes the number laiger than the other structure and CH3-C(CH3)2-CH3 is 2,2-dimethylpropane. 

Use Spartan View to step through the sequence of structures showing bond rotation in ethane and 2,2-dimethylpropane, and compute the energy difference between staggered and eclipsed conformations for each molecule. Which molecule has a larger energy difference, and why ... 

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. 

Figure 10.16 A mass spectrum of a branched alkane, 2,2-dimethylpropane, (CH3)4C. The structure is shown schematically in the figure. The hydrogen atoms are not shown.

---