How To Determine the Polarity of A Solventharding/summaries/14D06.pdf · How To Determine the...
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How To Determine the Polarity of A Solvent Useful Vocabulary: Polar: A structure having an uneven distribution of electron density. Dielectric Constant: A measure of a substance's ability to insulate charges from each other. Taken as a measure of solvent polarity, higher ε means higher polarity, greater ability to stabilize charges and reduced energy. Polar Solvent: A solvent with dielectric constant (ε) > 20. Nonpolar Solvent: A solvent with dielectric constant (ε) < 20. Polar covalent bond: A covalent bond in which the electron density is unevenly shared between the two bonded atoms, due to a difference in electronegativity or due to inductive effects. In general the electronegativity difference must be 0.5 or more before the bond is labeled as a polar covalent bond instead of nonpolar covalent bond. Steps to determine polarity of a solvent: 1. Count polar covalent bonds (bonds with EN difference greater than 0.5) and nonpolar covalent bonds to predict the dielectric constant (Remember: more polar bonds means higher dielectric constant) 3. Look at dielectric constant; if higher than 20, the solvent is polar and if it is lower than 20, the solvent is nonpolar Examples of polar solvents: Solvent # of Polar Bonds EN Difference of Polar Bonds # of nonpolar bonds Dielectric Constant Water 2 O-H = 1.4 0 80 Methanol 5 C-H= 1 C-O= 1 O-H= 1.4 0 32.7 Formamide 4 C-H- 1 C-0= 1 N-H= .9 1 (C-N) 111 N- Methylformamide 6 C-H= 1 C-O= 1 N-H= .9 2 (C-N) 36.7
Transcript of How To Determine the Polarity of A Solventharding/summaries/14D06.pdf · How To Determine the...
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
