How do we determine #D# and #L# terms, and how do they relate to absolute configuration?

Answer 1

#"D"# and #"L"# are archaic terms, and do not relate to absolute molecular geometry.

#"Dextrorotation"# and #"levorotation"# are terms that describe the experimental result. Rotation of plane-polarized light to the left or the right. This result has no necessary relationship with the chirality of a particular structure: i.e. a left-handed isomer may rotate clockwise, and a right-handed isomer may rotate counterclockwise.
We know that the #D# and #L# forms are optically active, and further, we know the direction of the optical rotation, but we do not know the absolute chirality. This notation was extensively used for sugars. Ordinary sugar, the stuff you put in your tea or sprinkle on your weet-bix, has several chiral centres, but it rotates plane-polarized light to the right as it approaches the observer, and so is #"dextrorotatory"#.
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Answer 2

for D or L form 1st of all draw the Standard Fischer projection of the molecule.

Standard Fischer projection is that which have its principle chain on the vertical line and the principle group at the top.
for making the same,

  • remember, you can do only EVEN NUMBER of changes at a #color(red) (PARTICULAR# chiral center , otherwise the molecule will optically
    changes.

    now, in the Fischer, look the configuration at bottommost chiral carbon. If H is in left, than it is D form, but if in right than it is L form.

    For R and S , 1st of all asign number(1,2,3,4) to the groups attached to chiral center according to the 'CIP rule' which says that
    number of a group #prop# 1/(molecular mass of the first atom

    attached to the chiral center)

    *if two groups are attached to the chiral centre with similar atom (here shown 'C' at 2,3 )than compare the mass of the atom next to them.

    Now, after numbering, check that the lowest number is farthest from you which can be done by putting it on the 'dash'( in dash wedge configuration) or on vertical line(in fischer projection) but remember
    you can do only EVEN NUMBER of changes at a #color(red) (PARTICULAR# chiral center , otherwise the molecule will optically changes. use the following mnemonics:

    now, considering whole as planar, WALK from #1rarr2rarr3#, if you follow clockwise path than it is R, but if anticlockwise than S. (use the mnemonics)
    ( i.e. the way you move your hand when write R and S)

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Answer 3

The D and L terms are determined based on the configuration of the highest numbered chiral carbon in a molecule. The designation is made by comparing the molecule to the chiral reference compounds, D-glyceraldehyde and L-glyceraldehyde. If the hydroxyl group on the highest numbered chiral carbon is on the right in a Fischer projection, the molecule is designated as D. If it's on the left, the molecule is designated as L. These terms relate to absolute configuration by indicating the spatial arrangement of atoms around the chiral carbon in the molecule.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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