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What does the Fischer projection do?
facilitates comparison of stereoisomers, holding them in their most symmetric conformation and emphasizing any differences in stereochemistry
Rotation of Fischer projection around 180 degrees?
- when we rotate a Fischer projection 180 degrees, the vertical (dashed) bonds still end up vertical and the horizontal (wedged) lines still end up horizontal
- it is allowed
Rotation of Fischer projection around 90 degrees?
- if rotated ninety degrees, the configuration changes
- the vertical bonds become horizontal and the horizontal bonds become vertical
- the molecule is different
- It is not allowed
Aside from not turning it ninety degrees, what else can we not do?
flip them over
The final rule for drawing Fischer projections helps to ensure that we do not __. This rule is what?
- rotate the drawing ninety degrees
- that the carbon chain is drawn along the vertical line of the Fischer projection, usually with the IUPAC numbering from top to bottom
How to draw mirror of Fischer projections?
interchanging the groups on the horizontal part of the cross reverses left and right while leaving the other directions unchanged
The __ can be applied to structures drawn using Fischer projections. The __ can also be determined directly from the Fischer projection, without having to convert it to a perspective drawing.
- R or S configuration
Explain the directions of the Fischer projection.
If te molecule demonstrates R, it is actually S when drawn in the regular structure
Fischer projections are most useful for what?
Asymmetric carbons are where?
The vertical lines and horizontal lines do what?
- compounds with two or more asymmetric carbon atoms
- the centers of crosses
- vertical go away
- horizontal go toward viewer
The carbon chain is placed where?
The entire projection can be rotated what?
Interchanging any two groups on an asymmetric carbon does what?
- along the vertical, with the IUPAC numbering from top to bottom
- 180 but nott 90 without changing the stereochemistry
- inverts its stereochemistry
We've defined __ as isomers whose atoms are bonded together in the same order but differ in how the atoms are directed in space. All other stereoisomers are classified as __, which are stereoisomers that are not mirror images. Most __ are either __ or compounds containing what?
- diastereomers x2
- geometric isomers
- compounds containing two or more chirality centers
One class of diastereomers are __, which are not mirror images of each others, making them diastereomers.
- cis-trans isomers
- (geometric isomers)
Cis trans isomerism is also possible when what?
there is a ring present
Apart from geometric isomers, most other compounds that show diastereomerism have what?
two or more chirality centers, usually asymmetric carbon atoms
A compound with n asymmetric carbon atoms might have as many as __ isomers. This formula is called the __.
What is the 2^n rule?
- n is the number of chirality centers (usually asymmetric carbon atoms)
- the 2^n rule suggests we should look for a maximum of 2^n stereoisomers
Compounds that are achiral even though they have asymmetric carbon atoms are called __.
What is the typical structure of them?
- meso compounds
- the two similar halves of the molecule have opposite configurations
In speaking of two diastereoisomers, the symmetric one is called the __, and the chiral one is called the __, since one enantiomer is __ and the other is __.
- meso diastereomer
- (±) diastereomer
an achiral compound that has chirality centers (usually asymmetric carbons)
The term meso was used to what?
describe an achiral member of a set of diastereomers, some of which are chiral
The optically inactive isomer seemed to be where between the what?
- in the middle
- dextrorotatory and levorotatory isomers