Carbohydrates

Question 1

empirical formula of carbohydrates

Answer 1

(CH2O)n

Question 2

n=1

Answer 2

methanal
previously names formaldehyde
toxic
CH2O

Question 3

n=2

Answer 3

hydroxyethanal
also names glycoaldehyde
CH(CH2OH)O

Question 4

n=3

Answer 4

constitutional isomers- can be aldose or ketose
glyceraldehyde
dihydroxyacetone

Question 5

constitutional isomers

Answer 5

same molecular formulae but differ in the order of attachment of atoms

Question 6

which sugar is used as the reference for determining the name of enantiomers of other sugars and why

Answer 6

glyceraldehyde
simplest chiral carbohydrate

Question 7

fischer projection- line meaning

Answer 7

vertical line means the molecules attached to the chiral centre are behind the plane
horizontal line means the molecules attached to the chiral centre are in front of the plane

Question 8

how to do a fischer projection

Answer 8

longest chain drawn vertically with the most oxidised carbon closest to the top (C=O)
the highest number chiral carbon determines the name, starting from the top.
D/L determined using glyceraldehyde as reference

Question 9

how to calculate how many isomers to expect

Answer 9

2^n
n=number of chiral carbons

Question 10

is D or L more common for sugars

Answer 10

D

Question 11

epimers

Answer 11

isomers that are not mirror images of each other
differ at one chiral carbon

Question 12

disasteriosomers

Answer 12

differ at more than one chiral carbon

Question 13

what is the most common ketofructose

Answer 13

(D-)fructose

Question 14

most common aldopentoses

Answer 14

D-ribose and D-2-deoxyribose

Question 15

saccharides in solution

Answer 15

monosaccharides with 5+ carbons form a ring where an oxygen bridge forms between the carbonyl carbon and a carbon further down

Question 16

5 membered ring

Answer 16

furanose ring
4 carbons and an oxygen

Question 17

6 membered ring

Answer 17

pyranose ring
5 carbons and an oxygen

Question 18

haworth projection

Answer 18

formation of ring forms an additional chiral carbon

Question 19

chirality of carbon 1 forms 2 new isomers named..

Answer 19

alpha and beta anomers
in solution, interchange between the two
equilibrium: 1/3 alpha 2/3 beta (none in linear form)

Question 20

alpha anomer

Answer 20

OH below plane of ring

Question 21

beta anomer

Answer 21

OH above plane of ring

Question 22

most energetically favourable form

Answer 22

beta anomer
all OH positioned furthest from each other
less steric hindrance

Question 23

how does the structure of rings reduce bond strain

Answer 23

kinks
chair and boat form

Question 24

is chair or boat less favourable

Answer 24

boat
steric crowding

Question 25

what are glycosaminoglycans

Answer 25

polymers that are highly hydrated
strong jelly

Question 26

how many chiral centres does glucose have

Answer 26

4

Question 27

fischer projection- D or L

Answer 27

OH on right=D
OH on left=L

Question 28

hemiacetal/hemiketal formation

Answer 28

aldehyde/ketone + alcohol
when the aldehyde/ketone react with an alcohol further along the chain this forms an intramolecular hemiacetal/hemiketal that creates a ring structure
oxygen bridge/glycosidic bond forms between OH and carbonyl