Alkanes results

Figure 7-1 shows the groups that are obtained for alkanes, and the corresponding notation of these groups as introduced by Benson [Ij. Table 7-2 contains the group contributions to important thermochemical properties of alkanes. Results obtained with these increments and more extensive tables can be obtained from Refs. [1] and [2]. 

The small differences m stability between branched and unbranched alkanes result from an interplay between attractive and repulsive forces within a molecule (intramo lecular forces) These forces are nucleus-nucleus repulsions electron-electron repul sions and nucleus-electron attractions the same set of fundamental forces we met when... 

What accounts for the stability of conjugated dienes According to valence bond theory (Sections 1.5 and 1.8), the stability is due to orbital hybridization. Typical C—C bonds like those in alkanes result from a overlap of 5p3 orbitals on both carbons. In a conjugated diene, however, the central C—C bond results from conjugated diene results in part from the greater amount of s character in the orbitals forming the C-C bond. 

The active oxidizing species is the 8 oxoiron complex formed on the action of the single-oxygen-atom donor. The interaction of 8 with the alkane results in hydrogen... 

The order of stability in highly fluorinated compounds is CF3 > CF2 > CF. The C-F bond of 1,2-difluoroalkanes is very unstable and hydrogen fluoride is readily eliminated in the presence of a base. Thus. 1.2-difluoroethane released hydrogen fluoride even at room temperature. The introduction of more than one fluorine into alkanes results in a stabilization of the C-F bond. Therefore, gcm-difluoroalkanes -CF2CH2- are inert towards weaker bases such as sodium hydroxide or sodium methoxide, and their dehydrofluorination requires stronger bases (r-BuOK or LDA) combined with a prolonged reaction time. 1,1-Difluoroethane is completely stable towards bases.15... 

Pentafluorosulfanylalkanes are also obtained by saturation of SF5-containing olefins. Dehydrohalogenation of SF5-alkanes results in the formation of SF5-alkenes, which can be converted to additional SF5-alkanes. 

We know from Sections 1.7 and 1.8 that an sp -hybridized carbon atom has tetrahedral geometry and that the carbon-carbon bonds in alkanes result from a overlap of carbon sp orbitals. Let s now look into the three-dimensional consequences of such bonding. What are the spatial relationships between the hydrogens on one carbon and the hydrogens on a neighboring carbon We ll see in later chapters that an understanding of these spatial relationships is often crucial for understanding chemical behavior. 

The small differences in stability between branched and unbranched alkanes result from an interplay between attractive and repulsive forces within a molecule (intramolecular forces). These forces are nucleus-nucleus repulsions, electron-electron repulsions, and nucleus-electron attractions, the same set of fundamental forces we met when talking about chemical bonding (see Section 1.12) and van der Waals forces between molecules (see Section 2.14). When the energy associated with these interactions is calculated for all of the nuclei and electrons within a molecule, it is found that the attractive forces increase more than the repulsive forces as the structure becomes more compact. Sometimes, though, two atoms in a molecule are held too closely together. WeTl explore the consequences of that in Chapter 3. 

For monomeric Ru carbonyl triphenylphosphine species as catalyst, optimum conditions are 120°C, 10 MPa of CO and Hj with benzene as solvent. For 1-hexene, 86% conversion results after 20 hr (2,000 ppm Ru) with 99% selectivity to aldehydes. The ratio of linear to branched aldehydes is 2.4 1. At al50°C, reduced conversions occur, owing to formation of inactive Ru complexes. High Hj partial pressures increase the reaction rate, but hydrogenation to alkane results. Excess triphenylphosphine gives improved selectivity for linear aldehyde, but at the expense of a drastic decrease in rate. 

Nanocrystalline MgO has demonstrated some unusual catalytic properties when chlorine gas is absorbed into the nanocrystals (Sun and Klabunde, 1999b). Contacts of this adduct with alkanes results in their catalytic chlorination see reaction (17.10). It appears that the chlorine is behaving in a manner more consistent with chlorine atoms being formed on the surface of the MgO by dissociative chemisorption. 

Removing a hydrogen from an alkane results in an alkyl substituent (or an alkyl group). Alkyl substituents are named by replacing the ane ending of the alkane with yl. The letter R is used to indicate any alkyl group. 

Similarly, bromination of 2,2,5-trimethyUiexane gives an 82% yield of the product in which bromine replaces the tertiary hydrogen. Chlorination of the same alkane results in a 14% yield of the tertiary alkyl chloride (Section 9.3). 

Becau.se of the weakness of this attraction, alkanes cxhihii relatively low melting points and boiling points relative to tho.se of more polar or chiirged molecules. The nonpolar nature of alkanes results in other physical consequences, such as rather limited ability to serve as solvents for polar compounds (remember... 

Figure 15.4 shows the yields of normal and branched alkanes resulting from high-viscous oil irradiation with 2 MeV electrons in two different modes (Zaikin et al. 2001). Mode 1 characteristic for a higher temperature and a higher dose rate of electron irradiation provided conditions for intense molecular destruction, while mode 2 appeared to be more favorable for isomerization reactions. 

The model substances for DSC were the same as those used for thermogravimetry (see section 3.1) such as the series of w-alkanes and some of the substances listed in ASTM D 2887-84. If an appropriate gas flow rate was used, then evaporation without residue of all the tested n-alkanes resulted, as already described for thermogravimetry. Fig. 3-39 demonstrates this behaviour for n-hexacontane. At a temperature of 99 °C there is a sharp fusion (melting) peak exhibiting a heat of fusion 243.3 J g. At 439 °C the maximum of energy resorption for the evaporation process appears, which has an onset temperature of 409 °C. The low energy resorption of 136 J g indicates the occurrence of an evaporation process. 

The reaction of OH radicals with alkanes results in the abstraction of a hydrogen atom followed by addition of oxygen whereby an alkylperoxy radical is formed In the reaction with alkenes OH is added to the double bond followed by addition of oxygen, generally at the neighbouring carbon atom. The peroxy radicals then enter into a reaction sequence of the type... 

Table 2.4 Increasing molecular weight of linear alkanes results ir melting and boiling temperatures increasing ...

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