HowToDeterminethePolarityofASolvent

UsefulVocabulary:Polar:Astructurehavinganunevendistributionofelectrondensity.DielectricConstant:Ameasureofasubstance'sabilitytoinsulatechargesfromeachother.Takenasameasureofsolventpolarity,higherεmeanshigherpolarity,greaterabilitytostabilizechargesandreducedenergy.PolarSolvent:Asolventwithdielectricconstant(ε)>20.NonpolarSolvent:Asolventwithdielectricconstant(ε)<20.Polarcovalentbond:Acovalentbondinwhichtheelectrondensityisunevenlysharedbetweenthetwobondedatoms,duetoadifferenceinelectronegativityorduetoinductiveeffects.Ingeneraltheelectronegativitydifferencemustbe0.5ormorebeforethebondislabeledasapolarcovalentbondinsteadofnonpolarcovalentbond.Stepstodeterminepolarityofasolvent:1.Countpolarcovalentbonds(bondswithENdifferencegreaterthan0.5)andnonpolarcovalentbondstopredictthedielectricconstant(Remember:morepolarbondsmeanshigherdielectricconstant)3.Lookatdielectricconstant;ifhigherthan20,thesolventispolarandifitislowerthan20,thesolventisnonpolarExamplesofpolarsolvents:Solvent #ofPolarBonds ENDifferenceof

PolarBonds#ofnonpolarbonds

DielectricConstant

Water 2 O-H=1.4 0 80Methanol 5 C-H=1

C-O=1O-H=1.4

0 32.7

Formamide 4 C-H-1C-0=1N-H=.9

1(C-N) 111

N-Methylformamide

6 C-H=1C-O=1N-H=.9

2(C-N) 36.7

References:Photo:http://packbackbooks.com/answers/1830088/How-do-polar-protic-solvents-affect-nucleophilicityhttp://web.chem.ucla.edu/~harding/index.html“Chemistry14DLectureSupplement,4thedition”HaydenMcNeil.2016.Print.SolventDielectricConstantValues:http://depts.washington.edu/eooptic/linkfiles/dielectric_chart[1].pdf