Twodimensional Nmr
A two-dimensional 2D NMR spectrum is a plot of NMR signal intensity as a function of two frequency variables, rather than just one as in a normal or one-dimensional spectrum. The frequency variables involved, which are determined by the nature of the pulse sequence, determine the specific type of two-dimensional spectrum produced. A two-dimensional spectrum is plotted either in a stacked plot Fig. 15.91a or, more commonly, a contour plot Fig. 15.91b . In this example, the first frequency...
Isoalkyl Group
The group remaining after the removal of one hydrogen atom from the methyl group at the nonbranched end of an isoalkane. Example. The structures shown in Fig. 5.16. h3c ch ch2 n-1 h3c-ch-1 h3c ch-ch2-1 Figure 5.16. a The general skeletal structure for an isoalkyl group, n 0, 1,2, b iso-propyl c isobutyl. The divalent triatomic grouping, CH2 consisting of one carbon atom and its two attached hydrogens . As the first part of the name implies, the methylene group may be considered as a derivative...
SUGGESTED READING Pgx
Bredt, J., Thouet, H., and Schmitz, J. Ann. 47, 219 1924 . This article contains the formal statement of what has become known as Bredt's rule, but Bredt's first article outlining the chemistry leading to the rule was published in 1902. Curl, R. F. and Smalley, R. E. Probing C60. Science 242, 1017 1988 . Ebbesen, T. W., ed. Carbon Nanotubes. CRC Press Boca Raton, FL, 1997. Fletcher, J. H., Dermer, O. C., and Fox, R. B., eds. Nomenclature of Organic Compounds. Advances in Chemistry Series 126...
Bornoppenheimer Approximation
The assumption that the total wave function of a molecule can be factored into an electronic wave function a vibrational wave function x, and a spin wave function s named after Max Born 1882-1973 and J. Robert Oppenheimer 1904-1967 . Example. Application of the Born-Oppenheimer approximation to the dipole strength expression Sect. 18.79 yields the integral Dj vKIVj Xi Xj 2 18.80 where the first integral evaluates the electronic wave functions over the electronic coordinates, and may be used to...
Isolobal Analogies
A concept introduced by R. Hoffmann who received the Nobel Prize in 1981 to provide a bridge between inorganic and organic chemistry. This bridge connects fragments of organometallic complexes with analogous fragments of methane in terms of the symmetry, energy, and electronic configuration of the respective frontier orbitals highest occupied and lowest unoccupied . One of the easiest ways to illustrate this relationship is to compare the isolobal fragment Mn CO 5 a d7 ML5 species with CH3....
Curtinhammett Principle
In a reaction where one product is generated by one conformer of the starting material while a different product is generated by a second conformer of the starting material, where both conformers rapidly interconvert and the products are kinetically controlled Sect. 12.86 , the product distribution is independent of the relative amount of each starting conformers. The product distribution is determined solely by the difference in free energy of activation AAG for the conversion of each of the...
Localization Energy
The decrease in delocalization energy involved in the removal of one or more orbitals from a delocalized n system of which it was a part. This theoretical process localizes n electrons, which were part of a conjugated system, onto a reduced set of carbon atoms in the system. Example. For benzene and its derivatives and other aromatics , the localization energy is a measure of the n energy change between the parent aromatic and the intermediate o complex in aromatic substitution reactions. Thus...
Pottbroche Process
The dissolution or dispersion of coal by heating at atmospheric pressure its suspension in an inert gas at 450 C in high boiling 350-450 C aromatic solvents. The mixture can be filtered while hot to remove ash and inerts, and the solvent recovered by vacuum distillation. It is uncertain whether a true solution or colloidal suspension is obtained by this treatment. The product is an ash-free high-Btu fuel. The process is named after the two German investigators who were largely responsible for...
Info Dbw
covalence, corresponds to the number of bonds attached to the atom in question. In the case of ions, the valence, more precisely called ionic valence, is the absolute charge on a monoatomic ion. Example. The valence of Mg is 2. The covalency of carbon in carbon monoxide, written as c O is 2, but in carbon dioxide, o c o , it is 4. The ionic valence of both Ca and O in CaO is 2. The word valence standing alone is rather ambiguous and the more precise terms such as ionic valence, covalence,...
Symmetric And Antisymmetric Behavior
If the sign of a wave function or direction of a vector associated with a molecule is unchanged upon application of a symmetry operation, the property is said to be symmetric with respect to that symmetry operation or the symmetry element associated with it . In contrast, if the sign of a wave function or direction of a vector associated with a molecule is reversed, but the magnitude is unchanged, the property is said to be antisymmetric with respect to the symmetry operation. Common...
Morse Curve 1
This is a plot, named after Phillip M. Morse 1903-1985 , showing the relationship between the potential energy Ep of a chemical bond between two atoms as a function of the distance between them. Example. The Morse curve for the hydrogen molecule is shown in Fig. 2.18. The minimum in the curve occurs at the equilibrium interatomic distance d0. At distances smaller than d0, the two nuclei repel each other and the potential energy Ep rises sharply at distances larger than d0, the Ep increases...
Dipole Moment
A vectorial property of individual bonds or entire molecules that characterizes their polarity. A diatomic molecule in which the electrons are not shared equally gives rise to a dipole moment vector with a negative end and a positive end along the bond connecting the two atoms. Therefore, such a molecule acts as a dipole and tends to become aligned in an electrical field. The electric dipole moment i see also Sect. 4.31 is obtained by multiplying the charge at either atom pole q in...