Sigma cr

A covalent bond is formed when an electron pair is shared between atoms. According to valence bond theory, electron sharing occurs by overlap of two atomic orbitals. According to molecular orbital (MO) theory, bonds result from the mathematical combination of atomic orbitals to give molecular orbitals, which belong to the entire molecule. Bonds that have a circular cross-section and are formed by head-on interaction are called sigma (cr) bonds bonds formed by sideways interaction ot p orbitals are called pi (77-) bonds. 

Sesquiterpenoid. 203, 1071 Sex hormone, 1082-1083 Sharpless, K. Barry. 734 Sharpless epoxidation, 735 Shell (electron), 5 capacity of, 5 Shielding (NMR). 442 Si prochirality, 315-316 Sialic acid. 997 Side chain (amino acid), 1020 Sigma (cr) bond, 11 symmetry of, 11 Sigmatropic rearrangement, 1191-1195... 

In the bond framework in Figure 10-18. all the bonds form from end-on overlap of orbitals directed toward each other. As illustrated by the three examples in Figure 10-20. this type of overlap gives high electron density distributed symmetrically along the intemuclear axis. A bond of this type is called a sigma (cr) bond, and a bonding orbital that describes a cr bond is a (7 orbital. 

In addition to these actions, glucocorticoids modify the function of several transmitters and/or their receptors, notably GABA, acetylcholine, noradrenaline, 5-HT and sigma (cr)-receptors for which the endogenous ligand is unknown. Conversely, the... 

The two kinds of covalent bond are not identical, one being a simple covalent bond, a sigma (cr) bond, the other being a stronger (but more reactive) bond called a n bond (p. 56). As in the formation of methane both elements attain noble gas configurations. We can consider the formation of ethene as the linking of two tetrahedral carbon atoms to form the molecule C2H4 represented as ... 

Covalent bonds are formed when atomic orbitals overlap. The overlap of atomic orbitals is called hybridization, and the resulting atomic orbitals are called hybrid orbitals. There are two types of orbital overlap, which form sigma (cr) and pi (tt) bonds. Pi bonds never occur alone without the bonded atoms also being joined by a ct bond. Therefore, a double bond consists of a O bond and a tt bond, whereas a triple bond consists of a ct bond and two tt bonds. A sigma overlap occurs when there is one bonding interaction that results from the overlap of two s orbitals or an s orbital overlaps a p orbital or two p orbitals overlap head to head. A tt overlap occurs only when two bonding interactions result from the sideways overlap of two parallel p... 

For an infinite set of data, the mean is designated by the lowercase Greek letter mu, p (the population mean), and the standard deviation is written as a lowercase Greek sigma, cr (the population standard deviation). We can never measure p and cr, but the values of x and 5 approach p and cr as the number of measurements increases. 

The designation sigma (cr) denotes that orbital overlap and electron density are greatest along the internuclear axis. 

Sigma (cr) bond (Section 1.6) A covalent bond formed by head-on overlap of atomic orbitals. 

Keywords Imidazoline (I) receptors PMS 812 2-BFI BU-224 BU-239 Benazoline Tracizoline Metrazoline Sigma (cr) receptors l-Phenyl-3-amino-tetralines (PATs) NE 100 Spipethiane... 

Figure 8-5 A schematic representation of the formation of a carbon-carbon doubie bond. Two rp -hybridized carbon atoms form a sigma (cr) bond by overiap of two sp orbitais (green, hatched) and a pi (tt) bond by overiap of properiy aiigned p orbitais (tan). Aii orbitais are fatter than shown here.

All the bonds in methane and ethane are sigma (cr) bonds because they are all formed by the end-on overlap of atomic orbitals. All single bonds found in organic am single bonds found in organic com-compounds are sigma bonds. pounds are sigma bonds. 

The carbons in ethene form two bonds with each other. This is called a double bond. The two carbon-carbon bonds in the double bond are not identical. One of the bonds results from the overlap of an sp orbital of one carbon with an sp orbital of the other carbon this is a sigma (cr) bond because it is formed by end-on overlap (Figure 1.16a). Each carbon uses its other two sp orbitals to overlap the s orbital of a hydrogen to form the C—H bonds. The second carbon-carbon bond results from side-to-side overlap of the two unhybridized p orbitals. Side-to-side overlap of p orbitals forms a pi (rr) bond (Figure 1.16b). Thus, one of the bonds in a double bond is a cr bond and the other is a rr bond. All the C—H bonds are a bonds. 

Side chain (of amino acid) the hydrocarbon group on an amino acid represented by H, CH3, or a more complex substituent. (22.6) Sigma (cr) bond a covalent bond in which the electron pair is shared in an area centered on a line running between the atoms. (9.1) Significant figures the certain digits and the first uncertain digit of a measurement. (1.4)... 

The most popular of these approaches is multiple regression analysis, introduced by Hansch in 1968. In this method, the most favoured variables are (i) partition coefficients (P), from the system octanol/water (ii) the sigma (cr) and rho (p) values derived from Hammett s Linear Free Energy Equation (Section 17.2) and (iii) Taft s steric factors E ) which are used to determine what space for substituents exists between a nominated small region of the lead molecule and its receptor (Section 16.2). These variables are correlated in the following equation ... 

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