Formaldehyde hybridization

For example, in formaldehyde, H2CO, one forms sp hybrids on the C atom on the O atom, either sp hybrids (with one p orbital "reserved" for use in forming the n and 7i orbitals and another p orbital to be used as a non-bonding orbital lying in the plane of the molecule) or sp hybrids (with the remaining p orbital reserved for the n and 7i orbitals) can be used. The H atoms use their 1 s orbitals since hybridization is not feasible for them. The C atom clearly uses its sp2 hybrids to form two CH and one CO a bondingantibonding orbital pairs. 

Bonding m formaldehyde can be described according to an sp hybridization model analogous to that of ethylene (Figure 17 2) According to this model the carbon-... 

FIGURE 17 2 Both (a) ethylene and (b) formal dehyde have the same num ber of electrons and carbon IS sp hybridized in both In formaldehyde one of the carbons is replaced by an sp hybridized oxygen Like the carbon-carbon double bond of ethylene the carbon-oxygen double bond of formaldehyde is com posed of a (T component and a TT component... 

Commonly used in biology as a tissue preservative, formaldehyde, CIDO, contains a carbon -oxygen double bond. Draw the line-bond structure of formaldehyde, and indicate the hybridization of the carbon atom. 

Like the carbon atoms in ethylene, the carbon atom in formaldehyde is in a double bond and therefore sp2-hybridized. 

In the formaldehyde molecule, H2CO, a double bond exists between the carbon and oxygen atoms, (a) What type of hybridization is involved (b) The molecule is found to be planar one bond between the C and O atoms is a cr bond, and the other is a rr bond. With a simple sketch, show the atomic orbital overlap that is responsible for the tt bond. 

The formaldehyde molecule is planar in its ground state (Figure 7-6). We first construct three strong a bonds involving thje carbon, the two hydrogen, and the oxygen atoms. Since the angles in the plane all are approximately 120°, we construct three equivalent orbitals in the xy plane which are directed from carbon toward Hx, H2, and O. For this purpose we hybridize the three carbon atomic orbitals 2s, 2px, and 2py. From three orbitals we can construct three linearly independent hybrid orbitals. 

On the oxygen we hybridize 2px and 2s as usual (see Figure 7-6) and form 2px - 2s and 2px + 2s. The a electronic structure for formaldehyde is shown in Figure 7-7, with a lone pair on O directed away from the carbon. 

The carbon-oxygen double bond in aldehydes and ketones is similar and can be described in either of these two ways. If we adopt the iocalised-orbital description, formaldehyde will have two directed lone pairs in place of two of the C-H bonds in ethylene. In this case the axes of these hybrid orbitals will be in the molecular plane (unlike the oxygen lone pairs in water). Either the components of the double bond or the lone pairs can be transformed back into symmetry forms. The alternative description of the lone pairs would he one er-type along the 0-0 direction and one jr-type with axis perpendicular to the 0-0 bond hut in the molecular plane. It is the latter orbital which has the highest energy, so that an electron is removed from it in. ionisation or excitation to the lowest excited state. 

PROBLEM 7.21 Describe the hybridization of the carbon atom in formaldehyde, H2C=0, and make a rough sketch of the molecule showing the orbitals involved in bonding. 

Rastogi and Bisht (Ref 3a) made combustion studies on hybrid propints consisting of o-s m-and p-toluidine nitTates with aniline-formaldehyde polymer as solid fuels, and red fuming nitric acid as oxidizer. They found that the results fitted a burning rate equation of the type, = a (G)v, where a and v are constants and G is the mass velocity. The authors conclude that the heterogeneous combustion reaction is diffusion controlled, and its rate is dependent on particle size... 

Speel, E. J. M., Saremaslani, P., Roth, J., Hopman, A. H. N., and Komminoth, P. 1998. Improved mRNA in situ hybridization on formaldehyde-fixed and paraffin-embedded tissue using signal amplification with different haptenized tyramides. Histochem. Cell Biol. 110 511-577. 

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