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Other examples include sugars (like sucrose), which have many polar oxygen–hydrogen (−OH) groups and are overall highly polar. If the bond dipole moments of the molecule do not cancel, the molecule is polar. For example, the water molecule (H 2 O) contains two polar O−H bonds in a bent (nonlinear) geometry.
[1] [2] The word hydrophobic literally means "water-fearing", and it describes the segregation of water and nonpolar substances, which maximizes the entropy of water and minimizes the area of contact between water and nonpolar molecules. In terms of thermodynamics, the hydrophobic effect is the free energy change of water surrounding a solute. [3]
Hydrophobic molecules tend to be nonpolar and, thus, prefer other neutral molecules and nonpolar solvents. Because water molecules are polar, hydrophobes do not dissolve well among them. Hydrophobic molecules in water often cluster together, forming micelles. Water on hydrophobic surfaces will exhibit a high contact angle.
Water is the most common and well-studied polar solvent, but others exist, such as ethanol, methanol, acetone, acetonitrile, and dimethyl sulfoxide. Polar solvents are often found to have a high dielectric constant, although other solvent scales are also used to classify solvent polarity. Polar solvents can be used to dissolve inorganic or ...
(However, PE only dissolves at temperatures well above 100 °C.) Poly(styrene) has a solubility parameter of 9.1 cal 1/2 cm −3/2 , and thus ethyl acetate is likely to be a good solvent. Nylon 6,6 has a solubility parameter of 13.7 cal 1/2 cm −3/2 , and ethanol is likely to be the best solvent of those tabulated.
A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for polar molecules, and the most common solvent used by living things; all the ions and proteins in a cell are dissolved in water within the cell. Major uses of solvents are in paints, paint removers, inks, and dry cleaning. [2]
The molecule increasingly becomes overall more nonpolar and therefore less soluble in the polar water as the carbon chain becomes longer. [5] Methanol has the shortest carbon chain of all alcohols (one carbon atom) followed by ethanol (two carbon atoms), and 1-propanol along with its isomer 2-propanol, all being miscible with water.
Note the decrease in ΔG ‡ activation for the polar-solvent reaction conditions. This arises from the fact that polar solvents stabilize the formation of the carbocation intermediate to a greater extent than the non-polar-solvent conditions. This is apparent in the ΔE a, ΔΔG ‡ activation. On the right is an S N 2 reaction coordinate diagram.