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Sigma symbol

This phenomenon is not possible in p-nitrobenzoic acid hence, p-nitrophenol is a stronger acid with respect to p-nitrobenzoic acid than is expected on the basis of a comparison of substituents in which this resonance delocalization is not an important factor. It was, therefore, recommended that Op = 1.27 be used for p-nitro derivatives of phenols and anilines, rather than the Op = 0.78 given in Table 7-10. These enhanced sigma constants, symbolized a, apply primarily to electron-withdrawing groups in reactions aided by low electron density at the reaction site. [Pg.320]

The electron density in both molecular orbitals is symmetrical about the axis between the two nuclei. This means that both of these are sigma orbitals. In MO notation, the Is bonding orbital is designated as eru. The antibonding orbital is given the symbol An asterisk designates an antibonding orbital... [Pg.651]

In this expression, the n are the amounts of each substance in the chemical equation and the symbol X (sigma) means a sum. The first sum is the total standard enthalpy of formation of the products. The second sum is the similar total for the reactants. [Pg.370]

Ionic conductivity is often given the Greek symbol kappa ( ) whereas electrical conductivity is given the different Greek symbol sigma (a). [Pg.302]

The term n is the number of measurements, and n - 1 is referred to as the number of degrees of freedom. The term s represents the standard deviation. The significance of s is that the smaller it is numerically, the more precise the data (the more the measurements are bunched around the mean). For an infinite number of measurements (where the mean is fl), the standard deviation is symbolized as o (Greek letter sigma) and is known as the population standard deviation. An infinite number of measurements is approximated by 30 or more measurements. [Pg.11]

Population Standard Deviation The dispersion of data around the mean for the entire population of possible samples (an infinite number of samples), which is approximated by n > 20, is called the population standard deviation and is given the symbol o (Greek letter sigma). [Pg.21]

Finally, the symbols + and written as superscripts to the A symbol, refer to two types of sigma states, 2+ and 2 . If the wavefunction is unaltered by reflection through a plane passing through the two nuclei, the state is positive (+) if it changes sign, it is negative ( —). [Pg.47]

The basis of the VSEPR theory is that the shape of a molecule (or the geometry around any particular atom connected to at least two other atoms) is assumed to be dependent upon the minimization of the repulsive forces operating between the pairs of sigma (a) valence electrons. This is an important restriction. Any pi (7t) or delta (8) pairs are discounted in arriving at a decision about the molecular shape. The terms sigma , pi and delta refer to the type of overlap undertaken by the contributory atomic orbitals in producing the molecular orbitals, and are referred to by their Greek-letter symbols in the remainder of the book. [Pg.84]

The Diels-Alder reaction is called a [4 + 2] cycloaddition because a ring is formed by the interaction of four pi electrons in the diene with two pi electrons of the alkene or alkyne. Since the electron-poor alkene or alkyne is prone to react with a diene, it is called a dienophile ( lover of dienes ). In effect, the Diels-Alder reaction converts two pi bonds into two sigma bonds. We can symbolize the Diels-Alder reaction by using... [Pg.684]

The substituent present on the left of the asymmetric carbon is denoted by the symbol p (rho) and if present on the right, then by the symbol o (sigma). [Pg.131]

This equation may seem quite complicated at first, but it is easier to apply once we understand the meaning of all the symbols. First of all, x, stands for the individual measurements made. There are 5 values of x, so i takes the values 1, 2, 3, 4, and 5. We thus have, in the first set of data, xi = 21, X2 = 24, X3 = 25, X4 = 26, and xs = 29. The quantity x is the average of these, which we have already established as 25. The number of data is , in this case 5. The symbol S (capital Greek sigma) represents a summation, so we simply add all the terms which appear to the right of it. It is easiest to do this using a table, as shown below. [Pg.26]

Here S is the symbol for the Greek letter sigma, and simply means take the sum of whatever follows, in this case the general term /(n). The n = 1 below E means start at this value while the N above denotes the final value of n. [Pg.84]

The term (p aO P a) is given the symbol a (sigma) and is constant for given substituents. Equation 2.3 thus simplifies to ... [Pg.32]

In this expression, values of n are the stoichiometric coefficients and the symbol S (sigma) means a summation. The procedure is to convert the reactants into the most stable form of their elements [-Z A//f (reactants)] and then recombine the elements into products [+S A//f°(products)]. [Pg.69]

The true (unknown, hypothetical) value of a property of the set is often called a parameter and given a lower-case Greek letter symbol. For example, the standard deviation of the population is symbolized by the Greek sigma The corresponding property determined in die... [Pg.433]

Figure 4.8 Summary of ways a filled orbital can stabilize a carbocation using sigma-type overlap. The arc symbolizes one or more CH2 groups. Most common is the onium ion shown on the top. Figure 4.8 Summary of ways a filled orbital can stabilize a carbocation using sigma-type overlap. The arc symbolizes one or more CH2 groups. Most common is the onium ion shown on the top.
Some texts will draw a circle in a six-membered ring to symbolize an aromatic. A semicircle with a plus may be also used to symbolize a sigma-complex. Don t use the circle notation when doing mechanisms, because it is so easy to lose track of electrons. [Pg.143]

C4. Enter Symbol for Each Variance Parameter eg PVsym(l) = Sigma C... [Pg.329]

Resonance structures are diagrammatic tools used predominately in organic chemistry to symbolize resonant bonds between atoms in molecules. The electron density of these bonds is spread over the molecule, also known as the delocalization of electrons. Resonance contributors for the same molecule all have the same chemical formula and same sigma framework, but the pi electrons will be distributed differently among the atoms. Because Lewis dot diagrams often cannot represent the tme electronic stmcture of a molecule, resonance stmctures are often employed to approximate the tme electronic stmcture. Resonance stmctures of the same molecule are connected with a double-headed arrow. While organic chemists use resonance stmctures frequently, they are used in inorganic stmctures, with nitrate as an example. [Pg.28]

The compact form of this result is obtained by the explicit use of the 3-1 symbol for comparison we refer to Hobson [(6), Sect. 88] where three expressions cover the particular case of Eq. (49) where all the p are sigmas or cosines. [Pg.272]

To save writing out the axis of symmetry, plane of symmetry or centre of symmetry in full each time we mention them, we give each of these symmetry elements a symbol. Thus a plane of symmetry is given the symbol o (sigma) and a centre of symmetry the symbol i. An /2-fold axis of symmetry is given the symbol C that is, a twofold axis is signified by C2, a threefold axis by C3, and so on. [Pg.83]

Instead of writing a series in the form used up to now, in which various terms are exhibited, we can use a standard symbol for a sum, a capital Greek sigma, which we introduced in Chapter 5. For example, the geometric series can be written as... [Pg.162]

Ans. Recall that in an atom there are three atomic p orbitals arranged perpendicularly to each other. When the p orbitals of two reacting atoms approach each other along the same axis (both are p or Py or Pj), they are said to be colinear. A covalent bond formed by the combination of colinear p orbitals is also called a sigma bond, as was the case of the combination of two atomic s orbitals. The symbol for a sigma bond formed by the combination of colinear p orbitals is... [Pg.61]

The symbol 51(sigma), means the sum of and n and m are the total of the coefficients of the products and mctants, respectively. To apply this generalization in this question, use the given values from the table and recall tet the standard enthalpy of formation for any element in its standard state is zero. Oxygen gas is an element in its omdard state, so no value is given in the table. [Pg.45]

Figure 6.16 Correlation of sigma values with rate of oxidation of phenolate anions by singlet oxygen. Open symbols indicate phenols with meta substituents and filled symbols, phenols with para substituents. Numbers indicate phenols listed in Table 6.13. [Reproduced with permission from P. G. Tratnyek and J. Hoigne, Environ. Set Technol. 25, 1596 (1991). Copyright 1991, American Chemical Society.]... Figure 6.16 Correlation of sigma values with rate of oxidation of phenolate anions by singlet oxygen. Open symbols indicate phenols with meta substituents and filled symbols, phenols with para substituents. Numbers indicate phenols listed in Table 6.13. [Reproduced with permission from P. G. Tratnyek and J. Hoigne, Environ. Set Technol. 25, 1596 (1991). Copyright 1991, American Chemical Society.]...

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See also in sourсe #XX -- [ Pg.186 ]

See also in sourсe #XX -- [ Pg.193 ]




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