Chemistry: Determining Solubility of Vitamins

[Mazurka]

1. The problem statement, all variables and given/known data

"Vitamins are important chemicals for survival. Vitamin A, Vitamin B6, and Vitamin C are three common vitamins. Simplified representations of their structures are given.

* See relevant equations.

Based on the functional groups that you can identify, which vitamins will be soluble in water? Explain your answer."

2. Relevant equations

http://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/All-trans-Retinol2.svg/500px-All-trans-Retinol2.svg.png

http://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Pyridoxine_structure_ver2.svg/200px-Pyridoxine_structure_ver2.svg.png

http://upload.wikimedia.org/wikipedia/commons/thumb/e/e7/L-Ascorbic_acid.svg/200px-L-Ascorbic_acid.svg.png

3. The attempt at a solution

Through some further research, I learned that while Vitamin B6 and C are both soluble in water, Vitamin A is only fat soluble. However, my struggle rests in the explanation as to why each of these vitamins is soluble in water or fat.

Vitamins B6 and C both have a fair number of hydroxide (-OH) bonds. Perhaps solubility in this case is determined by the number of hydrogen bonds that can form between the vitamin and its surrounding water molecules? It makes sense to me. However, if that is true, Vitamin A also possesses a hydroxide bond: Vitamin A should be soluble in water, to some degree.

I have not yet been taught how to read and comprehend any other part of the illustrated structures. I can only recognize hydroxide bonds. Perhaps there is another relationship between hydroxide bonds and solubility that I overlooked?

Please take into account that I am only at an intermediate high school level of education. I will not be able to understand any explanation that requires me to have attended a grade twelve or university level of chemistry. I greatly appreciate any help that can be provided.

Thank you,

Eric.

[Borek]

Back in seventies I was taught a simple mnemonic - FADEK are fat soluble.

Your approach is right - substances with lots of ionizable groups (carboxylic acids, amines) or those with lots of -OH groups are usually soluble in water. Vitamin A has a single -OH group and a very bulky, non-polar body - so its solubility will be very low.

In a way that's "similar dissolves similar" - polar substances are easily dissolved in polar solvents (like water), non-polar substances prefer non-polar solvents (like fat). This is only a rule of thumb and explanations are very hand-wavy - not based on any solid facts. But in many cases this approach works.