Physical properties and analytical chemistry Flashcards
Physical properties
Characteristics of matter that can be measure or observed without a change in chemical composition
Intensive property
- Not dependant on the amount of substance e.g. temperature
Extensive properties
Dependant on the amount of substance e.g. mass/volume
Dipole-dipole interaction
- Interactions between the postive end of one dipole and the negative end of another dipole
Vander waals forces
- Weak forces of attraction that exists between non polar molecules
- Distance dependant interaction which are induced dipole-dipole
Hydrogen bonding
- Attractive forces between H attached to an electronegative atom
Melting point
- Used to characterise organic compounds and confirm purity and melting point of pure compounds are greater than impure
Impure compound
- Increases the molecular weight but not regularity
Boiling point
Temperature when the vapour pressure of the liquid is equal to the atmospheric pressure state changes from liquid to gas
Wander waals forces
- Dependant on the area of contact between forces
- Increase as molecular size increases
- Greater amount of energy required to overcome the forces
- Branched alkanes are more compact so there is less surface area for force interactions
Boiling point and hydrogen bonding
- The -OH is strongly polarised with the pair of electrons in the O so having more oxygen groups increases the boiling point
Dipole-dipole atteraction and boiling point
- ## Polarised CO bond and non bonding electrons form a dipole moment
Carboxylic acid and boiling point
- Forms a stable hydrogen bonding dimer very high boiling point
Properties of H2O
- High polar solvent
- Excellent solvent for polor and ionic
- Poor solvent for non polar molecules
Hydrophilicity and lipophobicity
- Ability for chemical compound or drug to go into solution in H2O
- Polar and ionic and form hydrogen bonds and dipole-dipole with solvent and the fat is insoluable so it cannot cross the cell membrane
Hydrophobic and lipophilic
- Ability to chemical compound or drug to go into solution in lipids and non polar
- Are non-polar molecules, H2O insoluble, easily cross cell membrane, can enter target cells
- Biological membranes
Bond polarity and bond dipole moments
- Amount of charge x distance between charges
Polarity of a molecule
indicated by the molecular dipole moment of the entire molecule
Molecular dipole moment
Equal to the vector sum (sign is important) of the all individual bond dipole moments
Solubility
- Amount of a solute that can be dissolved in a specific solvent under given conditions. Measure of how much of the solute can be dissolved into the solvent at a specific temperature
Solvation or hydration
Dissolving solute in solvent
Polar Solute in a Nonpolar Solvent
Doesn’t dissolve
- Nonpolar molecules do not solvate ions very strongly
- Attractions of the ions in the solid for each other are much greater than their attractions for the solvent
Nonpolar Solute in a Nonpolar Solvent
Dissolves
- Molecules of a nonpolar substance weakly attracted to each other, and these van der Waals attractions are easily overcome by van der Waals attractions with the solvent
Nonpolar Solute in a Polar Solvent
Doesn’t disolve
- Nonpolar molecules are weakly attracted to each other little energy is required to break
- H2O molecules are strongly attracted to eachother due to hydrogen bonding
Substance added to pair of immicible solvents
- Distributes itself between the two solvents according to its affinity for each phase
- Polar compounds have greater affinity aqueous or polar phase
- Non-polar has a higher affinity to the non aqueous or organic phase
Partition law
- A given substance, at a given temperature, will partition itself between two immiscible solvents in a constant ratio of concentrations
- P = organic/aqueous
Partition coefficient
- Predict ADE of drugs within the body.
- Predict the onset of action of drugs or the duration of action of drugs,
- Calculate physical and chemical characteristics
How to calculate partition
- Unionised/organic = Organic
- Unionised/water = Aqueous
- Organic/aqueous = Partition coefficient
- % of drug = organic phase divided by total of drug
Weak acid or weak base
ionisation to form an anion or a cation alters the solubility profile of the drug
Experimantal partition coefficient
pH effect on partition coefficient
- Measure P of the unionised molecule
- P value for acids: measured at low pH when the acid is unionised
- P value for bases: measured at high pH to prevent ionisation
Apparent partion coefficent
fraction of unionised x true partion coefficient
Partition coeffient compartments
- Use 1-octanol collerates with in-vivo 8 carbon hydrophobic and OH is hydrophilic
- Aqueous buffer represents blood plasma in the body
Shake flask method
Obtaining organic solvent
- 2 phases are mixed together
- 2 phases seperate and the drug is added the flask is then shaken
- 2 phases are then allowed to seperate and the concentration of the drug the aqueous phase can be determied by spectroscopy or titration
- Concentration of Octanol phase found by subtrating value of P calculated
