Question

1. Thinking of the types of bonds present in a molecule of glucose, would you expect the glucose to be soluble in water? Why or why not? 2. What is needed for a carbon to be a chiral center for carbon)? Given an example that is NOT a monosaccharide and using the chart of aldoses and ketoses; how many chiral centers are there in a D-galactose molecule?

Answer 1

ANSWER 15 The glucose is- structural formula of OH OH OH OH -CH-CH CH-CH₂OH & helpe Although it is a covalent molecule, yet it is highly soluble in water (~910 g/L at 25°c). Quite obvious from the structure, glucose contauss 5 –OH groups which undergo an extensive H bond formation with water molecules which makes it highly soluble in water. The -CHO group also forms H-bonds to some extent in solubili- zation in water. Because glucose contains highly polar bonds (c=0 coo & 0-H), it has a very high dipole moment of 8.68 Debye. This means each molecule of gluose is involved in strong dipole-dipole interactions with Honoecules. This combined effects of H-bonding & dipole- dipole forces make glucose highly soluble in water.

ANSWER 2) chirality is the property of an object of it being non-superimposable on its mirror image. The object is said to be chiral. A molecule can be chiral if it has chival carbon(s). Infact, a molecule containing ONLY ONE chiral carbon is always optically acture (and molecule ir chiral as a whole). A chiral carbon is a sp3-hybridised (tetrahedral) carbon bonded to FOUR different groups/atoms. such a carbon is called chiral centre or stereo centre or asymmetric carbon. In the following example of chinal molecule, the chinal carbon is marked by '*'. Br clearly, Сн, -ен-ен-ең this chiral carbon is bonded to 4 different substituents i.e., CH₂, Br, H2 CH₂ CH2 which makes it non-superimposable on its mirror image.

In the Fischer projection of a molecule, the intersections of horizontal and vertical lines represent chiral carbons. As is visible in the rightside of the lowermost row of the above diagram, D-galactose has 4 chiral carbons marked by '*' in the diagram below:

ТЕ СТЕ ДА 75% і 11:20 CHO нон CH OH D-Glyceraldehyde сно но -н сно на-он HH OH CHOH D-Erythrose Н. -он CH2OH D-Threose сно CHO н——он нон нон CH2OH D-Ribode нон нон -он CH2OH D-Arabinose CHO -он HOGH н -он CH2OH D-Xylose CHO но -н но -н -OH Снон D-Lyxose CHO н но сно -он -н -Н CHO Hннон Hннан на-он нон CH2OH D-Allose СНО но -н н——он н сон H он CH2OH CHO H- OH HO н -OH H- CH2OH CHO но-НН но- -он -он CH,OH сно нон нонн нон н -он нон Н он Н -ОН CH2OH CH OH -н сно Нонн HO Hн H -ОН CH2OH HO- но- -ОН H — POH снуон D-Altrose D-Glucose D-Mannose D-Gulose D-Idose D-Galactose D-Talose

СНО кон HD — Н но в и |-он Сн, он D-Calactose