5.1 overview of isomers Flashcards
(16 cards)
Two things that have the same chemical formula but arent the same compound
* what are the two subdivisions of this
Isomers - meaning they have the same # of atoms in each compound - which is why their formuals are identical
Constitutional isomers
Steroisomers
Whats the other name for constitutional isomers?
* What are they
Also called structural isomers
They have different bond connectivities
Do stereoisomers have the same bond connectivitity?
Yes
These are molecules w/ the same formula and bonding patternt, but different 3D arragements
When you think about Cis and trans isomers what subdivision of isomers do they fall into?
Stereoisomers
so they have the same connectivity but in one the carbon is going down and in the other the cabron is going up, meaning their 3D arrangement varies
What kind of isomer is this?
Stereoisomer
* their connectivity is exactly the same, its 4 carbons bound w/ a pi bond connecting carbon 2 and 3
however their 3D shape varies
when you have a carbon-carbon double bond that means you have the sideways overlap of p orbitals making that bond
* if you try to rotate them to match you would break that sideways overlap of those p orbitals, breaking that pi bond and changing that connectivity
* so pi bonds can’t rotate
so the whole thing is that they have the same connectivity, but you can’t rotate it becuase of the pi bond, meaning they have different 3D structures
So in this picture theres a double bond so it can’t rotate. meaning no matter how you flip these they’re always going to be a different arrangement. Which one is cis and which one is trans?
The first one is cis becuase both hydrogens are on the same side of the double bond
The second one is trans because they’re on different sides of the double bond
NOTE: this only works w/ a double bond because they can’t rotate
NOTE: not all alkenes will be capable of cis and trans
* each sp^2 carbon (except for the double bond) has to be bound to two different things - so the carbon itself has to be bound to two different things
* In our case each carbon is bound to a methyl and a hydrogen, which are two different things, so were good
In the example below you can see the carbon on the right is bound to two different hydrogens so it doesnt work
Cis = same side
Trans = opposite side
Two immages that are mirror images of eachother, but not superimposable (not identical)
chiral
two objects that are mirror images and identical
achiral
* think a blank sheet of paper
So if they’re perfect mirror amges but nit superimposiable that means the have the same physical properties to they’re hard to dilinate between
When you have two molecules that are mirror images but non superimposable (chiral)
Enantiomers
* they’ll have the same physical properties as one another
Explain what a chiral center is
The chiral center is waht actually makes it a chiral
Chiral center is an sp^3 hybridized atom (likely carbon) which makes its tetrahedral in shape and has 4 different groups attached to it
if you have one of these centers that’s the greatest indication that a molecule will likely end up chiral
* an achiral molecule will likely have this center but bound to two of the same other substituents
so the wave i dilinate between enantiomers is the way the bend light. If one bends it to the right the other will bend it to the left
What is a racemic mixture
Solution that is 50:50 with two different enantiomers and is optically inactive (doesnt rotate light because they cancel eachother out)
Stereosiomers are a subdivision of isomers. What are our 2 subdivisions of stereosiomers?
Cis/Trans: They have the same formula, but either the two molecules above the double bond are the same or they’re different
Chiral centers: So they’ve got the same formula, however, they’re mirror images, but non superimposable (not identical) –> meaning they have a different 3D structure, however, they have the same formula
