hydrogen gas acetone substrates chemistry exothermic reaction atomic mass ammonia sodium diels alder reaction reagents equilibrium cesium single step derivatives junior chemistry methanol temperatures concentration chemical reactions chirality solvent organic solvents ethers molecules thymine cell cycles selectivity cis electrophile aspirin nucleophile transition state krebs cycle cytosine atomic weights journal article Organic cells acyl electron density catalyst presence racemic mixture phosphate catalytic hydrogenation reagent organic reactions metabolism organic chemistry carbons water molecules glucose atoms electron pair alkyne proteins molecule carbon atoms acids and bases local anesthetic living organisms hydrogen catalysts intermediates alcohol reactants activation energy pyruvate hydrogen peroxide amino acids chemicals room temperature hydrogen bonds byproducts chromosomes esters dehydration electron acceptor dehydration reaction protons neutrons and electrons heat flow synthesis joules atom alkene oxidation carbon dioxide correlation covalent bonds constituents alcohols alkenes dna molecule highest energy protons chemical reaction electrons isomer ketone salicylic acid