Alkanes three-bond

The three simplest alkanes. The bond angles in methane, ethane, and propane are all close to 109.5°, the tetrahedral angle. 

June et al. (85) presented united-atom calculations for butane and for hexane in silicalite, whereby the bond and dihedral angles of the alkanes were allowed to vary. In addition, the calculation of hexane took account of an additional intramolecular Lennard-Jones potential for nonbonded atoms more than three bonds apart (which prevents the alkane crossing over itself). The interaction parameters for the alkane molecules were taken from Ryckaert and Bellmans (3), and those governing the interaction of the alkanes with the zeolite from a previous study of the low-occupancy sorption of alkanes in silicalite (87). Variable loadings of alkanes were considered from 1 to 8 molecules per unit cell were considered, and calculations were allowed to run for 500 ps for diffusion at 300 K. 

Figure 5.2 provides the fluorine NMR of a typical linear CF3 alkane, that of 1,1,1-trifluorobutane. Its CF3 group appears as a triplet at -66.94 ppm with three-bond HF coupling of 11 Hz. 

Making Predictions A carbon atom in an alkane is bonded to four other atoms. In an alkene, a carbon in a double bond is bonded to three other atoms, and in an alkyne, a carbon in a triple bond is bonded to two other atoms. What geometric arrangement would you predict for the bonds surrounding the carbon atom in each of these cases (Hint VSEPR theory can be used to predict shape.)... 

The delta Platt number is defined as the Platt number of the isomer minus the Platt number of the corresponding alkane. (For n-alkanes the Platt number is n — 3.) The Platt number is the total number of groups of four carbon atoms three bonds apart [Platt, J. R.,/. Chem. Phys., 15(1947) 419 56(1952) 328]. This correction is used only for branched alkanes. 

Carboxylic Acids Carboxylic acids, R—C—OH, are named by dropping the -e from the alkane name and adding -oic acid however, many common names are used. For example, the four-C acid is butanoic acid (the carboxyl C is counted when choosing the root) its common name is butyric acid. Figure 15.15 shows some important carboxylic acids. The carboxyl C already has three bonds, so it forms only one other. In formic acid (methanoic acid), the carboxyl C bonds to an H, but in all other carboxylic acids it bonds to a chain or ring. 

The loss of a hydrogen would leave each carbon atom with only three bonds if nothing else occurred. Recall that the combining power of carbon is 4, not 3. The need for four bonds to each carbon is satisfied by the formation of a second bond between the two carbon atoms. The conversion of an alkane to alkene is an important industrial reaction. It is carried out by heating the alkane in the presence of a metal catalyst. Alkenes are important as intermediate compounds used in the manufacture of a host of plastics, textiles, mbbers, dmgs, detergents, and other commercial products. 

Similarly to our discussion of sp orbitals, the properties of the double bond are incompatible with the ground-state electronic structure of carbon. Three of the four bonds formed by carbon are equivalent to each other. These are or-bonds and are comparable in strength to the bonds in alkanes, which are also referred to as o--bonds. One of the three sigma bonds is used to join one carbon to another in the formation of the double bond. The geometry of these three bonds is the trigonal geometry, i.e., the three bonds lie in a flat plane with bond angles of 120° (Fig. 12-1). The fourth bond of each carbon of the double bond, used to form the second or 77-bond of the double bond, is weaker than a c-bond. 

Three distinct types of electrons are involved in valence electron transitions in molecules. First are the electrons involved in single bonds, such as those between carbon and hydrogen in alkanes. These bonds are called sigma a) bonds. The amount of energy required to excite electrons in cr bonds is usually more than UV photons of wavelengths >200 nm possess. For this reason, alkanes and other saturated compounds (compounds with only single bonds) do not absorb UV radiation and are therefore frequently very useful as transparent solvents for the smdy of other molecules. An example of such a nonabsorbing compound is the alkane hexane, CgH. ... 

Let us turn our attention toward the three major reactions of triplet carbenes in the presence of h3 drocarbons addition to olefinic C=C bonds, abstraction of hydrogen from CH bonds, and insertion into alkane CH bonds. 

Alkane, CH bonded to three other carbon atoms 6.78 0.57... 

The Nath, Escobedo, and de Pablo (NERD) force field [100,131-133] was developed to provide accurate predictions of thermodynamic properties. It is currently available for linear [100] and branched alkanes [131,133] as well as for alkenes [132]. It has a similar functional form as the TraPPE-UA force field, but bond stretching is included. This interaction and angle bending are represented by harmonic potentials [(20) and (22)]. The torsional potential is of the form of (25), neglecting cross terms. The U 12-6 potential (6) is used to describe the intermolecular and intramolecular interactions between sites that are separated by more than three bonds. The LJ parameters were obtained from fits to experimental values of liquid density and second virial coefficient. Saturated liquid densities from the NERD force field are in good... 

Three years after Green discovered the tetramethyl silane CH bond activation (reaction 5) [14], Bergman et al. [19] and Graham et al. [20] found independently, in 1982, the first examples of oxidative addition reaction of alkane CH bonds with formation of hydrido alkyl complexes (reactions 6 and 7). 

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