Tag Archives: D & L designation

Monosaccharides – ♪♪ That’s not my name ♪- putting name to structure

Standard

Continuing from where we left off introducing  carbohydrates and kicking it off with MONOSACCHARIDES :glucose and fructose, we venture deeper into the realm of Carbohydrates.

NOMENCLATURE OF SUGARS

D vs L Designation : ENANTIOMERS

Monosaccharide sugars are further categorized depending on their structure, in which they display stereoisomerism.

Looking at the structures of glucose and fructose, D&L designation is based on the configuration about the chiral/asymmetric carbon .

D-and-L-configurations-of-glucose

  • if more than one chiral center exists, D& L designation refers to the chiral center ( carbon in this case) furthest from carbonyl group.
  • if the -OH group is on the left on the furthest chiral carbon – L-designation

if – OH group is on the right on furthest chiral carbon – R-designation 

  • NOTE: in the image on the left, chiral carbons are denoted by *  and -OH in question is labelled. 

dl-fructose_num-svg

  • NOTE: – Observe, D & L designations are displays of stereoisomerism , the moleules are mirror images of each other, therefore 

groups on the RHS of one molecule is switched to the LHS  in the mirror image , and vice versa, not only the hydroxyl ( -OH) which determines D&L designation.

D & L designations are ENANTIOMERS of each other

 
   

******************************************************* D******D ********************

******************

**** ***************************************************************************************************************************************************After the sugars have been classified as D or L configuration, they differ once again as epimers, another form of optical isomerism********************

EPIMERS :  

two sugars that differ only in configuration around one C atom.   Simply put 🙂

Pentose and Ketose sugars can also cyclize from their straight chain  to form Haworth projections.

**********************************************************************************************************************

D-glucose cyclizes to give β-glucopyranose ring

  • D-glucose cyclizes : molecule bends so that C1 (anomeric carbon) reacts with C5, thus forming a ring structure
  • This results, forming a ring structure, for glucose. ——–>hemiacetal (in red) pyranose – 6  membered ring



************************************************************************************************************************************************************************************************************************************************************************************************************************************************


  • <———OR similarly for fructose, forming  a hemiketal(show in red)furanose-5 membered ring

********************************************************************************************************************************************************************************************************************************************

 6( or 5) carbon sugar   membered  ring structure ; Note fructose and glucose are both hexose sugars but their rings have different a number of sides.

monosac

*****************************************************************************************************************************************************************************************************************

******

Futher helpful links to these topics :
http://guweb2.gonzaga.edu/faculty/cronk/CHEM198pub/L07-index.cfm

http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/sugar.htm#deriv

Advertisements