You have a <u>true</u> or <u>full rhyme</u> when both the final consonant and the preceding vowel are repeated.
You have an <u>imperfect</u>, <u>slant</u>, or <u>half-rhyme</u> when the consonants of the ending syllable match, but the preceding vowels do not (or vice versa).
isomerism, the existence of molecules that have the same numbers of the same kinds of atoms (and hence the same formula) but differ in chemical and physical properties.