Transcript Organic for Chem II

UNIT 6
Theories of Covalent Bonding
and Intro to Organic Chemistry
Functional Groups and Organic
Nomenclature
3-D Structure
**You are responsible for being able to draw
accurate 3-D structures of relatively simple
organic compounds!**
 You must correctly show




all bond angles (this includes not “splitting” bonds)
which atoms are in the plane of the paper
which atoms are in front of the plane of the paper
which atoms are behind the plane of the paper
 Start practicing now
Carbon
Carbon has an exceptional ability to
bond with itself, forming a variety of
molecules with chains or rings of C
atoms.
Carbon also forms strong bonds with H,
O, N, and the halogens.
Consequently, C can form millions of
compounds.
Carbon
Carbon has 4 valence electrons and forms 4
bonds. These 4 bonds can be a combination
of single, double, and triple bonds.
methane, CH4
formaldehyde, CH2O
acetonitrile, CH3CN
Carbon
 Bond lengths: C—C > C=C > C≡C
 Bond strengths: C≡C > C=C > C—C
Carbon
 Hydrocarbons containing no multiple
bonds are not very reactive.
 Organic compounds get their reactivity
and their characteristics from functional
groups such as -OH (alcohol) and -COOH
(acid).
 Recognizing functional groups is a
“must.”
Alkanes and Cycloalkanes Have
no Functional Groups
Compounds that contain only C and H and only
single bonds are called either alkanes or, if the
C’s form rings, cycloalkanes. They have no
functional groups.
cyclohexane, a cycloalkane
hexane, a straight chain alkane
formula C6H14
formula C6H12
There Are Many Ways to Show
Organic Structures
• The structures shown on the previous slide are called
condensed structures or condensed structural formulas.
• Lewis structures show all bonds and all nonbonding
valence electrons.
Lewis structures
condensed structural formulas
Line Angle Structures
Organic compounds can be really large. Imagine
how many C’s and H’s and their bonds you’d
have to show: the structure would be very
“busy.”
Lewis structures
line angle structures
Line Angle Structures
Line angle structures are another way to represent
organic molecules, a way that lets you focus on
functional groups. No C’s are shown, and almost no
H’s bonded to C’s are shown, either.
Lewis structures
line angle structures*
*There is a C
atom at either
end of every
line segment.
The H’s on each
C are enough
to give the C
four bonds
total.
YOU MUST BE ABLE TO COUNT TO 4.
Functional Groups - Alkenes
• Clearly, line angle structures are less “busy.”
• C=C is the alkene functional group, also called
the carbon-carbon double bond.
Lewis structure
line angle structure
trans-2-hexene (The double bond starts
on carbon number 2. One counts from
the end that gets to the C=C bond first.)
cyclohexene
Which Carbon has the Functional
Group?
• Organic compounds are “read” and named from
the end that brings you to the functional group
first. All structures shown below are for the
same compound, trans-2-hexene.
Lewis structures
line angle structures
condensed structural formulas
Functional Groups - Alkynes
C≡C is the alkyne functional group, also known as
a carbon-carbon triple bond.
Lewis structure
line angle structure
2-hexyne (The triple bond starts on C number 2. One counts from
the end that gets to the carbon-carbon triple bond first.)
Functional Groups
Alkyl Halides
Alkyl halides (-X) all have a carbon atom
bonded to a halogen atom (F, Cl, Br, I).
Halogen atoms are designated X.
2-bromopropane or propyl bromide,
CH3CHBrCH3
Lewis structure
line angle structure
Functional Groups
Aromatic rings
• Several structures are aromatic, but we will look at only one:
the benzene ring, also called an aromatic ring.
• Benzene is NOT three alkenes! It is a unique structure
where six electrons are shared among all 6 carbon atoms.
That is why the line angle structure is often seen with a circle
in the middle of the ring.
Lewis structure
line angle structures
benzene, C6H6
Aromatic Hydrocarbons
 contain 6membered ring
structures with
alternating
double bonds,
stabilized by the
delocalized
electrons from
the pi bonds.
 are not as
reactive as the
alkenes and
alkynes.
Functional Groups
alkene
-X
halide
aromatic
ring
alkyne
Functional Groups - Alcohols
Alcohols all have the –OH group (called a
hydroxyl group and sometimes shown as
HO-).
Isopropyl alcohol or 2-propanol,
CH3CHOHCH3
Lewis structure
line angle structure
Ethers
• are like water, with alkyl groups
replacing both of the -Hs:
 H-O-H
 R-O-H
 R-O-R’
water
alcohol
ether
• are relatively unreactive.
• are commonly used as solvents.
Functional Groups - Amines
Amines are organic bases and have the
formula RNH2, RNR’R”, or RNHR’ , where R is
an alkyl group.
CH3CH2NH2
ethylamine
(CH3)3N
trimethylamine
pyrrolidine
All three functional groups in blue are amines.
Functional Groups
alcohol
ether
R = alkyl group, which is
a group containing C’s and
H’s with no multiple bonds.
amine (1°)
Some Aldehydes and Ketones
O
║
R-C-R'
O
║
R-CH
O
║
HCH
methanal
(formaldehyde)
C=O is called a carbonyl group
ketone
aldehyde
O
O
║
║
CH3CH CH3-CH2-CH
ethanal
(acetaldehyde)
propanal
O
║
CH3-C-CH3
propanone
(acetone)
Functional Groups Carboxylic Acids
Carboxylic acids (-COOH) are organic acids.
lauric acid,
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2COOH
Lewis structure
line angle structure
Note that the -OH
group and the =O
are on the same
C atom.
Functional Groups - Esters
The fats in our bodies are esters. Below is a
simple ester.
ethyl acetate,
CH3CO2CH2CH3
Lewis structure
line angle structure
The ester group is in green.
Although carbon and most
hydrogen atoms aren’t shown,
other atoms are.
Functional Groups
Amines, Amides, and Nitriles
amines
amides
 Amides are like amines, but with an adjacent C=O.
 Be careful! Both amines and amides have different forms:
primary (1°), secondary (2°), and tertiary (3°).
 Nitriles are R-CN.
Functional Groups
aldehyde
carboxylic acid
amide
- C≡N
nitrile
ketone
ester
Functional Groups
Circle and label each functional group.
alcohol
alkenes (5)
carboxyl group
vitamin A (retinol)
ester
aromatic ring…NOT
three alkenes!
aspirin
Functional Groups
Circle and label each functional group.
ester (3)
a triglyceride
alkenes (4), all cis
aromatic ring
estrogen
All -OH are alcohols. Note that some are written HO-.
3-D Structure
 Solid lines are bonds in the plane
of the board or paper.
 Wedges show bonds to atoms in
front of the plane.
 Dashed lines show bonds to atoms
behind the plane.
3-D Structure
**You are responsible for being able to draw
accurate 3-D structures of relatively simple
organic compounds!**
 You must correctly show




all bond angles (this includes not “splitting” bonds)
which atoms are in the plane of the paper
which atoms are in front of the plane of the paper
which atoms are behind the plane of the paper
 Start practicing now
3-Drawing Structure
Now, draw the 3-D structure for this compound.
CH3 CH2 CH2CH2COOH
Nomenclature
 Organic compounds get their reactivity
and their characteristics from functional
groups.
 Organic compounds are named after the
functional groups they contain.
 We will start with the alkanes.
Alkanes
 are characterized by stable C-C single
bonds
 are aka saturated hydrocarbons.
 are named for the number of carbons
in the longest chain.
 have no functional groups.
Alkanes
Molecular
formula
Condensed Structural Formula
CH4
CH4
C 2H 6
CH3CH3
C 3H 8
CH3CH2CH3
C4H10
CH3CH2CH2CH3
C5H12
CH3CH2CH2CH2CH3
C6H14
CH3CH2CH2CH2CH2CH3
C7H16
CH3CH2CH2CH2CH2CH2CH3
C8H18
CH3CH2CH2CH2CH2CH2CH2CH3
C9H20
CH3CH2CH2CH2CH2CH2CH2CH2CH3
C10H22
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Name
methane
ethane
propane
butane
pentane
hexane
heptane
octane
nonane
decane
Nomenclature
• Systematic naming comes from the
International Union of Pure and Applied
Chemistry (IUPAC).
• Below is the template you will use to build
the name of ANY organic compound.
stereomain
functional
substituents
unsaturation
isomerism
chain
group
Nomenclature of Alkanes
1. Find the longest
continuous chain of C
atoms, and use that as
the base name of the
compound.
2. If there is more than
one long chain, choose
the one that gives
more substituents.
3. Number the C atoms in
the longest chain,
beginning with the end
that brings you to the
substituent sooner.
4
1
5
CH3 - CH - CH3
|
2
CH3 - CH - CH2
3
|
CH3
Nomenclature of Alkanes
3. Name and give the location of each
substituent group.
Condensed Structural Formula
Name
CH3—
CH3CH2 —
CH3CH2CH2 —
CH3CH2CH2CH2 —
CH3CH2CH2CH2CH2 —
(CH3)2CH —
(CH3)3C—
methyl
ethyl
propyl
butyl
pentyl
isopropyl
t-butyl
Nomenclature of Alkanes
4. When two or more substituents are
present, list them in alphabetical order.
Condensed Structural Formula
Name
CH3—
CH3CH2 —
CH3CH2CH2 —
CH3CH2CH2CH2 —
CH3CH2CH2CH2CH2 —
(CH3)2CH —
(CH3)3C—
methyl
ethyl
propyl
butyl
pentyl
isopropyl
t-butyl
Nomenclature of Alkanes
CH3
|
7
5
CH3 - CH - CH2
6
|
3
4
CH - CH - CH2 - CH3
|
4
1
CH3
2
2,4-dimethylpentane
CH3
3-ethyl-2,4,5-trimethylheptane
1
CH3 - CH - CH3
|
2
CH3 - CH - CH2
3
|
|
CH3 CH - CH3
|
5
Drawing an Alkane from its Name
Draw the structure of 3-ethyl-2-methylpentane.
1. Write the backbone (pentane).
2. Put in each substituent at the correct C and
adjust the hydrogens to keep 4 bonds per C.
CH2 - CH3
|
CH3 - CH - CH - CH2 - CH3
|
CH3
Cycloalkanes
Hydrocarbons where some of the C
atoms form rings.
Reactive because of the strain
caused by the 60° bond angle.
Structural Isomers
Compounds
with the same
molecular
formula but
with different
bonding
arrangements
are structural
isomers.
Structural Isomers of Pentane
3-D Structures
Draw the 3-D structures of :
pentane
acetaldehyde, CH3CHO
Geometry of Alkanes
Rotation about a
C-C single bond is
relatively easy,
and it occurs very
rapidly at room
temperature.
Although we talk about straight-chain hydrocarbons,
the alkanes constantly undergo motions that cause
them to change their shape, like a chain being
shaken.