Hybridized States

Carbon Hybridization. The hybridization of the carbon atom from the ground state to the hybrid sp (or tetragonal) orbital state was described in Ch. 3, Secs. 2.2 and 2.3. It was shown that this hybridization accounts for the tetrahedral symmetry and the valence state of four with four 2sp orbitals arranged in a regular tetrahedron with equal angles to each other of 109° 28. The diamond structure is formed when carbon atoms are bonded to each other in the configuration (see Fig. 2.1 of Ch. 2).PI 

Silicon Hybridization. Hybridization of the silicon atom occurs in a manner similar to the tetragonal hybridization of the carbon atom to form a configuration of four 3sp orbitals also arranged in a r lar tetrahedron.1 1 Boron Hybridization. As shown in Table 7.1, the boron atom has only one valence electron in the ground state (2p ). Yet boron is never monovalent but always trivalent as the atom is hybridized.l 11 1 However, unlike the tetragonal hybridization of earbon and silicon, the boron hybrid ization is trigonal (sjp). It occurs as follows  

The 2s electrons are uncoupled and one is promoted to the 2p orbital to form three equivalent s[P- hybrid orbitals with three axes located in the same plane, each directed to the comers of an equilateral triangle and separated by the same angle of 120°. The covalent radius is not well defined and is estimated to be 0.085-0.090 nm. Since boron has four orbitals available for bonding and only three electrons, it is an electron-pair accq)tor and it tends to form multi-center bonds. 

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I 7,1 Empirical Approaches to the Calculation of Properties 7.1.2.1 Hybridization States... 

In Section 7.1.2 a method for the calculation of mean molecular polarizability was presented. Mean molecular polarizability can be calculated from additive contributions of the atoms in their various hybridization states in a molecule (see Eq. (6)). Mean molecular polarizability, a, expresses the magnitude of the dipole moment, fi, induced into a molecule imder the influence of an external field, E (Eq. (15))... 

An esliniaie of the hybridization state of an aioin in a molecule can be obtained from the group ol ihc periodic table that the atom resides in (which describes the number of valence elecironsi and the connectivity (coordination of the atom ). The IlyperChem default sch em e uses ih is estiin ate to assign a h ybridi/ation slate to all atom s from th e set (n ii 11, s, sp, sp, sp2-- and sp The special... 

Organic molecules are generally composed of covalent bonded atoms with several well-defined hybridization states tending to have well-understood preferred geometries. This makes them an ideal case for molecular mechanics parameterization. Likewise, organic molecules are the ideal case for semiempirical parameterization. 

Ethylene is planar with bond angles close to 120° (Figure 2 15) therefore some hybridization state other than sp is required The hybridization scheme is determined by the number of atoms to which carbon is directly attached In sp hybridization four atoms are attached to carbon by ct bonds and so four equivalent sp hybrid orbitals are required In ethylene three atoms are attached to each carbon so three equivalent hybrid orbitals... 

Section 2 20 Carbon is sp hybridized in ethylene and the double bond has a ct com ponent and a rr component The sp hybridization state is derived by mix mg the 2s and two of the three 2p orbitals Three equivalent sp orbitals result and their axes are coplanar Overlap of an sp orbital of one car bon with an sp orbital of another produces a ct bond between them Each carbon still has one unhybridized p orbital available for bonding and side by side overlap of the p orbitals of adjacent carbons gives a rr bond between them... 

The atoms in rnethylketene (C3H4O) are connected in the order and according to the geom etry shown (You can view this model in more detail on Learning By Modeling) Determine the hybridization state of each carbon and write a Lewis structure for this neutral molecule... 

All of these trends can be accommodated by the orbital hybridization model The bond angles are characteristic for the sp sp and sp hybridization states of carbon and don t require additional comment The bond distances bond strengths and acidities are related to the s character m the orbitals used for bonding s Character is a simple concept being nothing more than the percentage of the hybrid orbital contributed by an s orbital Thus an sp orbital has one quarter s character and three quarters p an sp orbital has one third s and two thirds p and an sp orbital one half s and one half p We then use this information to analyze how various qualities of the hybrid orbital reflect those of its s and p contributors... 

Try making a model of a hydrocarbon that contains three carbons only one of which is sp hybridized What is its molecular formula Is it an alkyne" What must be the hybridization state of the other two carbons (You will learn more about compounds of this type in Chapter 10 )... 

The sp hybrid state of nitrogen is just like that of carbon except nitrogen has one more electron Each N—H bond in NH3 involves overlap of an sp hybrid orbital of N with a li orbital of hydrogen The unshared pair of NH3 occupies an sp orbital... 

The number of neighbors is given by the molecular graph and the following rules determine a hybridization state for each atom in a molecule. 

As special cases to these radii, better values are used for the elements boron to oxygen for particular hybridization states. 

Alternatively, ions of any one selected m/z value can be chosen by holding the magnetic field steady at the correct strength required to pass only the desired ions any other ions are lost to the walls of the instrument. The selected ions pass through the gas cell and are detected in the singlepoint ion collector. If there is a pressure of a neutral gas such as argon or helium in the gas cell, then ion-molecule collisions occur, with decomposition of some of the selected incident ions. This is the MS/MS mode. However, without the orthogonal TOF section, since there is no further separation by m/z value, the new ions produced in the gas cell would not be separated into individual m/z values before they reached the detector. Before the MS/MS mode can be used, the instrument must be operated in its hybrid state, as discussed below. 

Structure. Ethylene is a planar molecule with a carbon—carbon bond distance of 0.134 nm, which is shorter than the C—C bond length of 0.153 nm found in ethane. The C—H bond distance is 0.110 nm, and the bond angles are [Pg.432]

By definition, members of this group have a vicinal arrangement of their electron-deficient centers. They may be conveniently considered according to their atom composition and the hybridization state of any carbon atoms involved. 

Examine the C—C bond distances in these substances. Is there a correlation with the hybridization states of the bonded carbons ... 

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