As you are studying to recognize SN1 SN2 E1 and E2 reactions, you will find yourself faced with a long checklist to help you determine which reaction takes place under a given set of conditions. One of these conditions includes understanding the role of the different organic solvents. In this article I will help you understand the difference between polar protic solvents and polar aprotic solvents.
A polar solvent, as the name implies, has 2 poles. A partially positive and a partially negative pole. This occurs when the solvent molecule is made up of atoms that while covalently bound, are not sharing the electrons equally among the bonding atoms. The more electronegative atom will pull the electrons towards itself resulting in a slightly negative charge or 'pole', while the less electronegative atom winds up with a partially positive charge or 'pole'
A Polar protic solvent, has polarity or partial charge as described above. It also has the capability to hydrogen bond. Hydrogen bonding occurs when an H atom is bound to a highly electronegative nitrogen, oxygen, or fluorine atom. Since these atoms are highly electronegative, their polar bonds are so extreme, that hydrogen is left positive enough to attract another electronegative atom from the solution for a partial bond. Organic solvents typically do not contain fluorine, and so your polar protic solvents are molecules that have H bound to oxygen or nitrogen. Examples include water H2O and ammonia NH3
And finally we have polar aprotic solvents that fall into the polar category but cannot hydrogen bond. These solvents have are made up of atoms that have polar covalent bonds resulting in an uneven sharing of bonding electrons with partially charged poles. However, even if these solvents may contain a hydrogen atom, they are incapable of hydrogen bonding. This happens when the H atoms in the solvent are not directly bound to a nitrogen oxygen or fluorine atom.
A common example of a polar aprotic solvent is DMSO which stands for dimethyl sulfoxide. The condensed structural formula for the polar aprotic DMSO is CH3S=OCH3. In this solvent we have a pi bond between oxygen and sulfur, where the pi electrons are concentrated around the partially negative oxygen. The hydrogen atoms here are on carbon and unable to participate in hydrogen bonding due to lack of polarity in their non-polar covalent bond
A polar solvent, as the name implies, has 2 poles. A partially positive and a partially negative pole. This occurs when the solvent molecule is made up of atoms that while covalently bound, are not sharing the electrons equally among the bonding atoms. The more electronegative atom will pull the electrons towards itself resulting in a slightly negative charge or 'pole', while the less electronegative atom winds up with a partially positive charge or 'pole'
A Polar protic solvent, has polarity or partial charge as described above. It also has the capability to hydrogen bond. Hydrogen bonding occurs when an H atom is bound to a highly electronegative nitrogen, oxygen, or fluorine atom. Since these atoms are highly electronegative, their polar bonds are so extreme, that hydrogen is left positive enough to attract another electronegative atom from the solution for a partial bond. Organic solvents typically do not contain fluorine, and so your polar protic solvents are molecules that have H bound to oxygen or nitrogen. Examples include water H2O and ammonia NH3
And finally we have polar aprotic solvents that fall into the polar category but cannot hydrogen bond. These solvents have are made up of atoms that have polar covalent bonds resulting in an uneven sharing of bonding electrons with partially charged poles. However, even if these solvents may contain a hydrogen atom, they are incapable of hydrogen bonding. This happens when the H atoms in the solvent are not directly bound to a nitrogen oxygen or fluorine atom.
A common example of a polar aprotic solvent is DMSO which stands for dimethyl sulfoxide. The condensed structural formula for the polar aprotic DMSO is CH3S=OCH3. In this solvent we have a pi bond between oxygen and sulfur, where the pi electrons are concentrated around the partially negative oxygen. The hydrogen atoms here are on carbon and unable to participate in hydrogen bonding due to lack of polarity in their non-polar covalent bond
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For specific examples of these solvents types and how they relate to substitution and elimination reactions watch my youtube tutorial video on Polar Protic, Aprotic, Non-Polar Solvents
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