Structural isomers

✴ Structural Isomer - molecule with same molecular formula but with different arrangement of atoms✴ Differences in shape of isomers leads to differences in their physical and chemical properties

Structural Isomers

✴ For example, glucose, galactose and fructose have same molecular formula (C6H12O6) but different structures

glucose galactose fructose

dissolve

d in water

glucose

β-glucose

α-glucose

dissolved in water

✴ In dry state, glucose has linear structure, but when dissolved in water, molecule folds on itself to form one of two possible ring structures:

✴ Glucose itself has 3 different structural isomersI

✴ Small structural difference leads to large difference in chemical properties

✴ Two isomers of glucose differ only in orientation of a single hydroxyl (-OH) group

dissolve

d in water

glucose

β-glucose

α-glucose

dissolved in water

✴ Starch found in mushrooms (amylopectin) is a polymer of α-glucose - can be easily digested

starch - digestible

✴ Cellulose (found in celery) is a polymer of β-glucose - can’t be digested by most animals

cellulose - not digestible

✴ Isomers illustrate that structure of a molecule determines function of that molecule

Structure = Function