Zigzag conformations of alkanes

Z (stereochemical prefix), 173—175, 199 Z (symbol for atomic number), 7 Zaitsev, Alexander M., 184 Zaitsev s rule, 184, 191, 199, 200 Zidovudine, 1098 Ziegler, Karl, 246, 569 Ziegler-Natta catalyst, 246, 383, 567-570 Zigzag conformations of alkanes, 97 Zinc... 

Section 3 3 Higher alkanes adopt a zigzag conformation of the carbon chain m which all the bonds are staggered... 

The above method for calculating 8 v) was applied to the R v) spectrum in Figure 8.4c. Then, the n(v) and k v) spectra were calculated by the use of Equations (8.4a) and (8.4b), and the results obtained are shown in Figure 8.5. The k(v) spectrum has the shape of an absorption spectrum, from which band positions can be accurately determined. The bands observed at 2919 and 2850 cm are, respectively, due to the CH2 antisymmetric and symmetric stretching vibrations characteristic of the all-trans planar zigzag conformation of the -alkane chain. The doublet bands at 1471 and 1462 cm are assigned to the CH2... 

The number (nj) of the cross ct conjugations of the trios of a C-C bond and two antiperiplanar C-H bonds is important for the stabilities of alkanes. The cross conjugation number (nj) of an alkane is defined as that of the conformer where the longest C-C chain has trans a zigzag structure. For example, there are three cross conjugations (n = 3) in isobutene and none in n-butane (n = 0) (Scheme 27). Isobutane is more stable than n-butane [34, 35]. 

Every branched or unbranched alkane chain is built as a zigzag chain. When a chain contains three or more C atoms a part of the molecule can turn freely around a single bond in relation to the rest of the molecule. In a spontaneous process the molecule converts from one three-dimensional structure to another. According to a chemists the molecule changes from one conformation into another . Figure 3.15 is a representation of an alkane chain and two conformations of the same molecule. 

Analysis of the conformations of other alkanes can be done in a similar manner. For any linear alkane the most stable conformation is the so-called zigzag conformation, which is anti about all of the carbon-carbon bonds. The zigzag confonnation for hexane follows ... 

In a combined experimental and theoretical study, Borovkov et alP examined the properties of w-alkane radical cations in solution. Here, we shall just focus on one single aspect of their work, i.e., the conformers of one of the alkanes, w-nonane, C9H2o-In its simplest form of the highest symmetry, its structure can be described as a zigzag chain formed by the 9 carbon atoms. To each of the carbon atoms, 2 hydrogen atoms... 

Table 4.14 Structure (top) and physical properties [41] table below) of semi-fluorinated n-alkanes (60-63) and the homologous dialkyl bicyclohexyl liquid c stals 64 and 65 from which they are structurally derived. The spacefill model of 63 shows the helical conformation of the central perfluoroalkylene segment in contrast with the pentyl side-chains with their typical hydrocarbon zigzag conformation. The differences in charge distribution (red and blue denote negative and positive partial charges, respectively) are visualized by mapping of the electrostatic potential on to the electron density of 63 (B3LYP/6-31C //PM3 level of theory) [44, 50].

The higher alkanes resemble butane in their preference for anti and gauche conforma-Conformations tions about the carbon-carbon bonds. The lowest-energy conformation for any straight-Of Hi Cl her Alkanes c la n alkane is the one with all the internal carbon-carbon bonds in their anti a conformations. These anti conformations give the chain a zigzag shape. At room... 

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