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