The Key to Survival Why is this so important Over and over again you will be asked to do reactions the details to which you will receive in lecture and via your textbook For each reaction reagents will be used to convert one functional group into another ID: 918799
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Slide1
Identifying Functional Groups
The Key to Survival
Slide2Why is this so important?
Over and over again, you will be asked to do reactions, the details to which you will receive in lecture and via your textbook. For each reaction, reagents will be used to convert one functional group into another.
If you cannot recognize what a functional group looks like, it will be impossible for you to do this process… The facts that you need to remember won’t mean anything… And you won’t be able to draw the right pieces on your molecules…
Slide3What is a “functional group”?
A functional group is any collection of bonded atoms that are not simply sp
3
C-sp
3
C (your basic C-C single bond) or sp
3
C-H.
The only family in organic chemistry that has only C-C and C-H single bonds is the alkane family and they are recognized by their LACK of functional groups (or functionality, if you will).
Slide4Why is this necessary?
Knowing your functional groups will make your life much easier when its time for you to identify them in a lab assignment (Infrared Spectroscopy) or when you have to remember facts, like the reaction of an alkene with water and a catalyst forms an alcohol. If you don’t know what an alkene or alcohol looks like, this class is impossible.
Slide5In order to identify the functional groups, you have to know what sorts of bonds are in each kind of functional group.
We’ll scroll through the functional groups, one at a time and compare and contrast, until you (hopefully) get used to what they look like.
Just remember, organic professors are devious – and sometimes the mere change from a
zig-zag
structure to a condensed formula can entirely confuse you!
Slide6Alkanes
Just for comparison’s sake, let’s start with something that has no functional groups. Alkanes have C-C single bonds and C-H bonds and all the carbons are sp
3
hybridized. All of the following showing below are alkanes. Those in rings are still alkanes, and are referred to as cycloalkanes but they don’t have functional groups either.
Slide7Alkyl Halides
The alkyl halide is identified by the presence of an sp
3
C-X bond in the structure. Halides can be fluorine, chlorine, bromine or iodine (X=F,
Cl
, Br or I). Each of the following has an alkyl
halide (or more specifically, alkyl bromide, alkyl chloride, alkyl iodide, if you wish):
Slide8Alkenes
An alkene has a C=C in its structure. This C=C might have carbon groups or hydrogen atoms attached. Each of the following are alkenes:
Slide9Alkynes
An alkyne has a triple bond between two carbon atoms in its structure. Triple bond might have carbon groups on both or perhaps
one carbon group and one
hydrogen atom
attached (usually not drawn!).
If there are two carbon groups attached,
an
“internal alkyne
”
. Note the linear structure, as should be the case for
sp
hybridized carbon atoms.
Slide10Alkynes
An alkyne has a triple bond between two carbon atoms in its structure. If there is one carbon group
attached (and one hydrogen atom),
the functional group
is still called
an alkyne and we fine-tune the identification by calling it a “terminal alkyne”:
Slide11Arenes or Aromatic Rings
An
arene
or aromatic ring, for the purpose of this introductory course, is a six-membered ring of carbon atoms, with alternating double and single bonds. It can have up to six groups attached to it
. These may also be called “aryl” groups.
The following are examples of aromatic rings:
Slide12Ethers
The
ether is
identified by the presence of
C-O-C bond
in the structure.
The carbon groups on the left and right side can be alkyl groups or aryl groups but they cannot be carbonyls (C=O). Each of the following is an ether:
Slide13Epoxides
The
epoxide is a specific type of ether functional group, and contains the C-O-C bond inside a three-membered ring. Each of the following is an epoxide:
Slide14The amine
functional group has
a
nitrogen
atom.
The nitrogen atom can have two hydrogen atoms (NH
2
), one hydrogen atom and one carbon group (NHR) or two carbon groups (NHR
2
or NHRR’).
The carbon groups CANNOT be C=O (carbonyl). Note
how each of the following has
a nitrogen:
The Amine
Slide15What is what?
One of the following is an alkyl halide, one is an ether and one is an
amine.
Identify which is which.
Slide16What is what?
One of the following is an alkyl halide, one is an ether and one is an
amine.
The ether has the oxygen surrounded by carbons. The alkyl halide has the HALIDE and the
amine has the nitrogen atom.
Slide17What is what?
One of the following is an alkene, one is a terminal alkyne and one is an internal alkyne. Assign the structures to their type of functional group.
Slide18What is what?
One of the following is an alkene (with a double bond) and the others have triple bonds. They are alkynes. The alkyne in the middle of the chain is the internal alkyne and the other, at the end of the chain, is the terminal alkyne.
Slide19The Carbonyl Compounds
There are a whole series of compounds that contain the carbonyl group, C=O. The classification of the functional group is dependent upon what is attached to either side of the carbon atom of the carbon group. Identify what is attached to the left and right sides of each of the following:
Slide20The Carbonyl Compounds
The first compound has
OH
on the left and
C
on the right.
The second compound has
C
on the left and
C
on the right.
The third compound has
C
on the left and
H
on the right.
Slide21The Ketone (
NOT
KE
Y
TONE)
The ketone functional group has a carbonyl group, C=O, surrounded by carbon groups on both sides. They can be alkyl groups or aromatic rings
. The condensed formula for a ketone group is –C(O)-. Note
how each of the following has carbon groups on both the left and the right:
Slide22The Aldehyde
The aldehyde functional group has a carbonyl group, C=O, surrounded by a carbon group on one side and a H atom on the other. The carbon group can be alkyl or aromatic
. The condensed formula for an aldehyde is –CHO.
Note how each of the following has a carbon group on one side and a hydrogen atom on the other:
Slide23Can you tell them apart?
Which of the following is the aldehyde and which is the ketone?
Slide24Can you tell them apart?
The compound on the left is the aldehyde functional group (see the H on the right of the carbonyl?) and the compound on the right is the ketone (two carbon groups attached).
Slide25The Carboxylic Acid
The carboxylic acid functional group has a carbonyl group, C=O, surrounded by a carbon group on one side and a hydroxyl group, OH, on the other. The carbon group can be alkyl or aromatic. Note how each of the following has a carbon group on one side and an –OH on the other:
Slide26Can you tell them apart?
Which of the following is the aldehyde and which is the carboxylic acid?
Slide27Can you tell them apart?
The compound on the left is the aldehyde functional group (see the H on the right of the carbonyl?) and the compound on the right is the carboxylic acid (carbon on right, OH on left).
Slide28Can you tell them apart?
Identify which of the following is the carboxylic acid, aldehyde and ketone:
Slide29Can you tell them apart?
Identify what’s on either side of the carbonyls:
Slide30The Ester (
NOT
EST
H
ER)
The ester functional group has a carbonyl group, C=O, surrounded by a carbon group on one side and an OR’ group on the other. Either carbon group, attached to the C=O or on the O atom, can be alkyl or aromatic. Note how each of the following has a carbon group on one side and an OR on the other:
Slide31Can you tell them apart?
Identify which of the following is the ketone and which is the ester?
Slide32Can you tell them apart?
Identify what’s on either side of the carbonyls:
Slide33Can you tell them apart?
Note the difference between an ester and an ether. Esters have an OR group
attached to a carbonyl
. Ethers do not.
These are the two most confused functional groups!
Slide34Can you tell them apart?
Does the following molecule contain an ester or an ether?
Slide35Can you tell them apart?
With the OR group on the C=O, this is an ester.
What about this molecule? Does it have an ester?
Slide36Can you tell them apart?
With the OR group NOT on the C=O, there is not an ester in this molecule. Notice that this has TWO
different functional
groups, a ketone on the left and ether on the right.
Slide37The Acid Halide
The acid halide functional group has a carbonyl group, C=O, surrounded by a carbon group on one side and an –X atom on the other. X is typically a chloride or bromide. Note how each of the following has a carbon group on one side and an X on the other:
Slide38The Acid Anhydride
The acid anhydride functional group has two carbonyl groups, C=O, surrounding a central oxygen atom, and carbon groups on the other sides of the carbonyls. The carbon groups can be the same or different. Note how each of the following has the two carbonyl groups, surrounding an oxygen atom:
Slide39Can you tell them apart?
Which is an ester and which is an acid anhydride?
Slide40Can you tell them apart?
Note the identifying characteristic of the double carbonyl in an acid anhydride. An ester only has one carbonyl (C=O).
Slide41Can you tell them apart?
Which is an alkyl halide and which is an acid halide? Both have halides (in this case, bromides) but what makes them different?
Slide42Can you tell them apart?
The acid halide has its chloride or bromide attached directly to a carbonyl group (C=O). The alkyl halide has an sp
3
hybridized carbon (alkyl group) attached to the halide.
Slide43The Nitrile
The nitrile functional group has a C-N
triple
bond, and the nitrogen has a lone pair. Its commonly mistaken that the nitrogen atom has an undrawn hydrogen atom but that would be an error
in both
structure and thought
. The condensed formula for a nitrile is –CN.
Each of the following contain a nitrile:
Slide44Can you tell them apart?
Which is an alkyne (terminal, internal) and which is a nitrile?
Slide45Can you tell them apart?
The nitrile has a nitrogen atom in its triple bond. The other two are alkynes. The alkyne at the end of the chain is the terminal one (with a typically unseen hydrogen now shown) while the one in the center of the chain is the internal alkyne.
Slide46The Nitro
The nitro functional group is typically drawn as one of two possible equivalent resonance forms (they look alike), containing one N=O and one N-O. The
condensed formula
for a nitro group is NO
2
. Note how each of the following has a nitro group:
Slide47So there you go…
You
ha
ve
now seen all of the functional groups commonly encountered in organic chemistry. There are others lurking out there but if you know THESE, you are in really great shape… Now go try that problem set to double check yourself!