Select the word or phrase that complete each sentence (const…

Select the word or phrase that complete each sentence (constitutional isomers, diastereomers, enantiomers, meso compounds, higher, lower, reaction, addition, carbocation, carbanion, nucleophile, electrophile, elimination, heterolysis, homolysis, reagent, substitution, stronger, weaker, charge, activation energy, enthalpy, entropy, catalyst, transition state, intermediate,  concerted, two step, SN1, SN2, E1, E2, racemization, hyperconjugation, alkyl halides, inversion):     On an energy diagram, each valley represents a(an) ……………………………..  Complete word/phrase and correct spelling (verbatim) is required. No partial credit.