Final answer:
The magnitude of an ester's dipole moment is smaller because dipole-dipole interactions are weaker than ion-dipole interactions. These dipole interactions fall off more rapidly with distance, and induced dipoles resulting from temporary changes in electron density also exhibit relatively weak attraction.
Step-by-step explanation:
The magnitude of an ester's dipole moment is typically smaller than that of some other molecular dipoles due to the nature of its structure and the distribution of electron density within the molecule. When comparing the interactions such as ion-dipole and dipole-dipole interactions, we must take into account the strength and range of these forces. Ion-dipole interactions involve a full ionic charge and a dipole, and these forces decrease with distance following a 1/r2 relationship. Dipole-dipole interactions are weaker because dipoles have less charge than ions, and the attractive interaction between dipoles decreases faster than ion-dipole interactions, following a 1/r3 distance relationship.
Furthermore, temporary or induced dipole interactions (such as London dispersion forces) are considerably weaker and fall off with a 1/r6 dependence. Induced dipoles are a result of instantaneous fluctuations in electron density within molecules like helium atoms, where these temporary dipoles induce dipoles in adjacent atoms. Despite the weakness of these interactions, they are significant in the behavior of nonpolar molecules and noble gases.