Hydrogen Bonding SWBAT: Draw hydrogen bonds between two molecules

Definition Hydrogen Bond  A hydrogen bond is an electromagnetic attraction - not a true bond!  Hydogen must be directly bonded to a small atom with high EN (N, O, F)  Can form with another molecule (intermolecular) or another part of the same molecule (intramolecular).  The hydrogen has a partial δ + charge and the oxygen has a partial δ - charge from being covalently bonded to an electronegative atom

Symbol  Covalent bond: solid line  H-bond: dotted line

Intermolecular H Bonding  Hydrogen bonding between two molecules – from the attraction of the dipoles

Intra molecular H-bonding DNA  Hydrogen bonding within its own molecule – from the attraction of the dipoles

Intra…..3D- Structure of Proteins

Hydrogen Bonding

Important  H-bonds do not have to involve water molecules!  All it needs is a δ + H which can come from any molecule:  S H 2, C-O H, COO H, DNA, proteins….  And a δ - element as a neighbor (usually its O, S, N, P or the Halogen group)

Beryllium Chloride (tri-hydride)  BeCl 2 3H 2 O

Organic molecules and H- bonds  Draw dipole and partial charges of the following functional groups: don’t forget the unpaired Valence e- of Oxygen  COH Alcohol  CHO Aldehyde  CO Ketone  COOH Acid

H-Bond Drawing guide  Oppose each δ + and δ - with one H 2 O  Show the δ + and δ - and net dipole of each water molecule  Draw H-bonds as dotted lines Practice:  CH 3 COH 3H2O  CH 3 CH 2 COOH 4H2O  CH2O 2H2O