Bonding sigma bonds

Gassman, P.G. Fentiman Jr., A.F. J. Am. Chem. Soc., 1969, 91, 1545 1970, 92, 2549. For a discussion of the use of the tool of increasing electron demand to probe neighboring-group activity by double bonds, sigma bonds, and aryl rings, see Lambert, J.B. Mark,... 

Sigma (a) bonds Sigma bonds have the orbital overlap on a line drawn between the two nuclei, simple cubic unit cell The simple cubic unit cell has particles located at the corners of a simple cube, single displacement (replacement) reactions Single displacement reactions are reactions in which atoms of an element replace the atoms of another element in a compound, solid A solid is a state of matter that has both a definite shape and a definite volume, solubility product constant (/ p) The solubility product constant is the equilibrium constant associated with sparingly soluble salts and is the product of the ionic concentrations, each one raised to the power of the coefficient in the balanced chemical equation, solute The solute is the component of the solution that is there in smallest amount, solution A solution is defined as a homogeneous mixture composed of solvent and one or more solutes. 

A e-bond (sigma-bond) forms when the bonding pair of electrons are localized directly between the two bonding atonts. Since the electrons in a o-bond are as close as possible to the two sources of positive charge (the two nuclei), a o-boml has the lowest energy and is the most stable form of covalent bond. Thus o-bonds are strong. A o-bond is always the first type of covalent bond to be formed between any two atoms a single bond must be a c-bond. 

Alkanes, also called paraffins or aliphatic hydrocarbons, are hydrocarbons in which the C atoms are joined by single covalent bonds (sigma bonds) consisting of two shared electrons (see... 

Alkenes contain a C=C double bond. The C=C double bond can be described with two different models. According to the most commonly used model, a C=C double bond consists of a <7- and a tr-bond. The bond energy of the a-bond is 83 kcal/mol, about 20 kcal/mol higher than the tr-bond (63 kcal/mol). The higher stability of <7 bonds in comparison to n bonds is due to the difference in the overlap between the atomic orbitals (AOs) that form these bonds. Sigma bonds are produced by the overlap of two spn atomic orbitals (n 1,2,3), which is quite effective because it is frontal. Pi bonds are based on the overlap of 2,pz atomic orbitals, which is not as good because it is lateral or parallel. 

Sigma antibonding Pi antibonding Nonbonding Pi bonding Sigma bonding... 

When orbitals overlap, bonds form. When the overlap is along the internuclear axis, this is known as a a (sigma) bond. Sigma bonds can form between s, p, or hybridized orbitals. When the overlap is between parallel orbitals that lie perpendicular to the nuclear axis, this is known as a it (pi) bond. 

Because single bonds (sigma bonds) are more stable than pi bonds, the most common reactions of double bonds transform the pi bond into a sigma bond. For example, catalytic hydrogenation converts the C = C pi bond and the H—H sigma bond into two C—H sigma bonds (Section 7-7). The reaction is exothermic (AH° = about -80 to -120 kJ/mol or about -20 to -30 kcal/mol), showing that the product is more stable than the reactants. 

In alkanes or saturated hydrocarbons, each carbon atom forms four covalent bonds. These bonds are C —C and C — H sigma bonds. Sigma bonds are very strong, so for this reason, alkanes are also known as paraffins which means "inert". 

The sideways" bonds shown in Figure 3.20 are called pi (pronounced like pic) bonds. Sigma bonds are stronger than pi bonds, which leads us to the following rule ... 

Single bonds (sigma bonds) will also be seen in the carbon-oxygen bonds discussed later in the alcohol series, where there is a C-O-H bond. Double bonds (sigma and pi bonds) also occur in aldehydes and ketones where there is a C==0 bond. These homologous series will be looked at in Module 7. 

The carbon-hydrogen and carbon-carbon bonds have the same general electron distribution, being cylindrically symmetrical about a line joining the atomic nuclei (see Fig. 3.1) because of this similarity in shape, the bonds are given the same name, a bonds sigma bonds). 

In this section, we focus on the mode by which orbitals overlap—end to end or side to side—to see the detailed makeup of covalent bonds. These two modes give rise to the two types of covalent bonds—sigma bonds and pi bonds. WeTl use valence bond theory to describe the two types here, but they are essential features of molecular orbital theory as well. 

Ethene, propene and butene are planar compounds. The first bond on the unsaturated carbon atoms are sp hybrids, and these bonds are arranged as far apart in space as possible (i.e. at 120 degree in the same plane). These are s bonds (sigma bonds) and arc... 

All flexible macromolecules must contain at least a sequence of linear, covalently bonded atoms. The understanding of the cylindrically symmetric, directed, covalent bonds (sigma bonds) was thus the first step towards polymer science. This step was already taken in 1858 by Kekuld as shown in Fig. 1.8. The detailed structures of large aggregates of atoms (macromolecules) could next be analyzed in detail after X-ray diffraction was fully understood. Major steps in the development of X-ray analysis of macromolecules are listed in the figure. First, rigid macromolecules such as metals, salts, minerals, and ceramics were analyzed. This was followed by many polymer crystal structures and even globular proteins. 

The orbital in the hydrogen molecule is cylindrically symmetric along the H—H internuclear axis. Such orbitals are called sigma (sigma bond. Sigma bonds may also be formed by the overlap of an s and a p orbital or of two p orbitals, as shown in Figure 1.4. ... 

Sigma bond Sigma bond is formed by the end-to-end overlap of atomic orbitals along the molecular axis. This is also known as axial or head-on-overlap. 

In the valence-bond theory, covalent bonds are visualized as resulting from the overlap of atomic orbitals, resulting in two general t) es of bonds, sigma bonds and pi bonds. 

An orbital pointing toward an adjacent orbital is called a sigma orbital), and the bond involving the cr orbitals of two atoms is called a o- bond (sigma bond the Greek letter a is analogous to s). Thus in methane the four tetrahedral orbitals of the carbon atom are a orbitals, and the four C—H bonds are cr bonds. 

Figure 2.11. The sp hybrid orbital bonding (sigma bond) showing covalent bonding.

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