Properties ofwaterSolidlessdensethanliquidExpandsassolidifiesH-bondstosimilarextentasliquid(about15%moreH-bondsinsolid)Meansfishesdon'tfreeinlakes
Properties of water Solid less dense than liquid • Expands as solidifies • H-bonds to similar extent as liquid (about 15% more H-bonds in solid) • Means fishes don’t free in lakes
Water forms hydrogen bonds with polar solutesHydrogenbondsreadilyformbetweenanelectronegativeatom(the hydrogen acceptor) and a hydrogen atom covalently bondedtoanotherelectronegativeatom (thehydrogendonor)HydrogenacceptorHydrogendonore
Water forms hydrogen bonds with polar solutes Hydrogen bonds readily form between an electronegative atom (the hydrogen acceptor) and a hydrogen atom covalently bonded to another electronegative atom (the hydrogen donor)
Biologically important hydrogen bondsBetween theBetween peptideBetween thehydroxyl groupcarbonylgroupgroups inof an alcoholofaketonepolypeptidesand waterand waterHydrogen atoms covalentlybondedtocarbonatomsdonotparticipate in hydrogen bondingAlcohols,aldehydes,ketones,andcompoundscontainingN-Hbonds all form hydrogen bondsBetweencomplementarybasesofDNAwith H,OAdenine
Biologically important hydrogen bonds Hydrogen atoms covalently bonded to carbon atoms do not participate in hydrogen bonding. Alcohols, aldehydes, ketones, and compounds containing N-H bonds all form hydrogen bonds with H2O
ExamplesofH-bonddonors/acceptorsBetweentheBetweentheBetweenpeptidehydroxylgroupcarbonylgroupgroupsinof analcoholofaketonepolypeptidesandwaterandwaterR1R2RkacceptorsHNdonors
Examples of H-bond donors/acceptors
Hydrogen bondsBoth covalent and H-bonds involved in hydrogen bondinginteraction.H atom “tugged" between 2 electronegative atomsOnlyHatomwillwork(onlyHnucleus small enoughto approachlonepaire-cloud)Ho+H8+H-bondOIHx8+
Hydrogen bonds Both covalent and H-bonds involved in hydrogen bonding interaction. H atom “tugged” between 2 electronegative atoms. Only H atom will work (only H nucleus small enough to approach lone pair e-cloud)