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By kapil on Tuesday, - 01:02 am:
methanol,THf,acetone&acetonitrilwhich is more polor &why pl give incereasing orderof polarity
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By Chris Pohl on Tuesday, October 21, 2003 - 09:26 am:
The answer to your question depends somewhat upon your intended use of these solvents. For normal phase applications, the most polar of the solvents listed is acetonitrile. Burdick and Jackson have, or at least used to have a nice solvent handbook which lists the polarity index for these solvents as acetonitrile: 5.8, methanol: 5.1, acetone: 5.1 and THF: 4.0. But if you look at the elutropic value on alumina you get the following values: methanol is the most potent at 0.95, acetonitrile: 0.65, acetone: 0.56 and THF: at 0.45. A physical parameter which correlates roughly with the polarity index is the dipole moment of these solvents. The dipole moments for the solvents are: acetonitrile: 3.44, methanol: 2.87, acetone: 2.69 and THF: 1.75. Another physical parameter which correlates roughly with the polarity index is the dielectric constant. The dielectric constant for these solvents are: acetonitrile: 37.5, methanol: 32.7, acetone: 20.7 and THF 7.58. Of course, in reversed phase work methanol is invariably the weakest eluent followed by acetonitrile which is weaker than THF (I don't have any experience with acetone so I couldn't place it in this sequence for reversed phase elution power), so obviously more than just polarity is involved in this order reversed phase elution power.
methanol,THf,acetone&acetonitrilwhich is more polor &why pl give incereasing orderof polarity
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By Chris Pohl on Tuesday, October 21, 2003 - 09:26 am:
The answer to your question depends somewhat upon your intended use of these solvents. For normal phase applications, the most polar of the solvents listed is acetonitrile. Burdick and Jackson have, or at least used to have a nice solvent handbook which lists the polarity index for these solvents as acetonitrile: 5.8, methanol: 5.1, acetone: 5.1 and THF: 4.0. But if you look at the elutropic value on alumina you get the following values: methanol is the most potent at 0.95, acetonitrile: 0.65, acetone: 0.56 and THF: at 0.45. A physical parameter which correlates roughly with the polarity index is the dipole moment of these solvents. The dipole moments for the solvents are: acetonitrile: 3.44, methanol: 2.87, acetone: 2.69 and THF: 1.75. Another physical parameter which correlates roughly with the polarity index is the dielectric constant. The dielectric constant for these solvents are: acetonitrile: 37.5, methanol: 32.7, acetone: 20.7 and THF 7.58. Of course, in reversed phase work methanol is invariably the weakest eluent followed by acetonitrile which is weaker than THF (I don't have any experience with acetone so I couldn't place it in this sequence for reversed phase elution power), so obviously more than just polarity is involved in this order reversed phase elution power.
