Molecular structure molecules Hybridization Isomers

The two isomers of but-2-ene are stereoisomers because they have exactly the same constitution but a different spatial arrangement of their atoms in space. As we learned in Section 11, a double bond between C atoms consists of the overlap of hybrid orbitals to form a a bond and the sideways overlap of p orbitals to form a tt bond. Because of the ir bond, rotation about a double bond is severely restricted. Molecule (a) cannot be converted into molecule (b) simply by twisting one end of the molecule through 180°, so the two molecules are distinctly different above. To differentiate these two molecules, we call molecule (a) ds-but-2-ene and we call molecule (b) trans-but-2-ene. Because of differences in their molecular structures, the compoimds have different physical properties. For example, the melting points are —139 °C for ds-but-2-ene and —106 °C for tr ns-but-2-ene the boiling points are 3.7 °C for cis-but-2-ene and 0.9 °C for trans-but-2-ene. 

Examples of the various practical applications of dipole moments include, but are not limited to differentiation between isomers cis and trans, o, m, and p, tautomers, etc ), conformational analysis, studies of molecular geometry, supporting evidence for resonance hybrids, information about the polar character of molecules (important for solubility in different solvents and permeability through membranes), information about electrical effects of substituents (inductive, resonance), studies of hydrogen bonding, and studies of donor-acceptor interactions (e g., charge transfer complexes). Practical cases describing the use of dipole moments for different types of structural studies mentioned above can be found in numerous publications mentioned in this chapter. 

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