Q5 P. - Organic Chemistry (Mcmurry)

Question

Ethylene glycol,, may look nonpolar when drawn, but an

internal hydrogen bond results in an electric dipole moment. Explain.

Step-by-Step Solution

Answer

Ethylene glycol look non polar because the bond polarities of two carbon-oxygen bond cancel each other. So the dipole moment of ethylene glycol is zero.

Dipole moment

A dipole moment is defined as a measurement of the separation of the two opposite electrical charges. Dipole moments are a vector quantity. The magnitude is equal to charge multiplied by the distance between the charges and the direction is from negative charge to positive charge.

                                                                     $\mathrm{\mu }=\mathrm{q}\times \mathrm{r}$

Where $\mathrm{\mu }$ is the dipole moment, q is the charge, and r is the distance between the charges.

Dipole moment in Ethylene glycol

                                                                  Ethylene glycol

The dipole moment of ethylene glycol looks zero because the bond polarity of two carbon- oxygen bond cancels.

Whenever a hydrogen atoms get bonded to atoms like oxygen it acquires aformal positive charge and oxygen a formal negative charge. This is because oxygen is more electronegative and will tend to have greater share of bonded electrons. Hydrogen atom in one molecule (with formal positive charge) gets attracted toward the oxygen (with formal negative charge) either within the molecule (intramolecular) or in other molecule leading to hydrogen bonding (intermolecular). Thus polarization of electrons in a bond take place that induces a moment in the molecule.