How To Know When To Draw Wedges And Dashes

Chirality and Enantiomers

Before talking well-nigh the enantiomers, permit's go over the concept of mirror images and particularly when it pertains to organic molecules.

Any object has a mirror image. No tricks or magic here – just put a mirror in front of anything and you'll see its mirror image:

The key here is that some objects are non the same every bit their mirror images. The simplest example is our hands. They may look identical, but you won't be able to swap them without having the fingers on different positions or orientations.

Another instance would be the glasses shown above. They are the same as their mirror image simply if we replace i of the lenses with a dark lens, the mirror paradigm is now different – you cannot replace the glasses with the mirror image. It does not repeat the object in infinite because the position of the lenses is dissimilar.

In chemical science, the word for describing mirror image existence identical or different is "Superimposable".

If the object and its mirror image are the same, they are superimposable, if these 2 are not the same then they are non-superimposable images. Any object that is non-superimposable to its mirror prototype is said to be Chiral.

The same goes for molecules: Chiral molecules are not superimposable on their mirror epitome. Achiral molecules are superimposable to their mirror images which indicates that the mirror image is the same chemical compound.

Stereogenic Eye – Origin of Chirality

Nigh oftentimes, the origin of chirality in organic molecules is the presence of an asymmetric carbon. This is a carbon with iv different groups (atoms) also referred to equally a stereogenic center or a chiral(aty) eye.

If we draw the mirror image of this molecule, nosotros will see that it is non-superimposable to it. And here is ane new definition to larn:

If ii molecules are nonsuperimposable mirror images, they are called Enantiomers.

Enantiomers are types of stereoisomers since all the atoms are connected the same but they have a different 3D orientation.

A little scheme as a reminder about ramble isomers and stereoisomers. It too mentions the diastereomers, but you tin can ignore those for now if you have not covered them in your class:

Getting dorsum to the asymmetric carbon and chirality – A molecule tin can accept more than than one chirality centre and if y'all demand to place those, remember that you are looking for a carbon (even though information technology is not restricted to carbons only) with four unlike groups.

For example, these are the chirality centers in each of the following molecules:

To recognize the chiral center, look for the wedge and dash bonds as usually these are the ones indicating a chiral center.

One important thing to remember, a carbon with a double bond cannot be a chiral center every bit information technology does not have iv dissimilar groups. Yes, it has four bonds merely that is the standard valency of the carbon. It must have four different group south, therefore it must have a tetrahedral geometry.

How to Describe Enantiomers

In general, the easiest fashion to draw the enantiomer of a given molecule is to simply redraw the chemical compound, replacing all dashes with wedges and all wedges with dashes.

This is not a universal solution though because the wedge and dash representation is relative and depends on the direction nosotros are looking from. To know for sure if two molecules are enantiomers, the Cahn-Ingold-Prelog system (R and South) is used.

Another style of cartoon the enantiomer of a given molecule, is to put an imaginary mirror and depict everything reflected and this will too give y'all the enantiomer:

All the same, attention! – Yous should non exercise both: you lot should not draw the mirror reflection and change the wedges and dashes together with information technology, since you will end upwards having the same molecule:

You should either keep the molecule as it is and change every wedge to a dash or you can place a mirror paradigm anywhere (on the side, on the top, below, in forepart or behind) adjacent to the molecule and draw its reflection.

Do the following problems and cheque the next post on the R and Due south configuration, to double check your answers.

For each of the following pairs of compounds, determine the relationship between the 2 compounds: Are they enantiomers or the aforementioned chemical compound drawn differently? If you lot hesitate, determine the absolute configuration of chiral centers (if any:R or S).

answer

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Solution

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By joining Chemistry Steps, you will gain instant access to the answers and solutions for all the Practice Bug including over twenty hours of trouble-solving videos, Multiple-Choice Quizzes, Puzzles, and t he powerful set of Organic Chemistry ane and 2 Summary Study Guides.