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.

CarbonCarbon 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.

hexane, a straight chain alkaneformula C6H14

cyclohexane, a cycloalkaneformula 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.

condensed structural formulasLewis structures

Line Angle StructuresOrganic 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.”

line angle structuresLewis structures

Line Angle StructuresLine 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.

line angle structures*Lewis 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.

line angle structureLewis structure

cyclohexene

trans-2-hexene (The double bond starts on carbon number 2. One counts from the end that gets to the C=C bond first.)

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.

line angle structuresLewis structures

condensed structural formulas

Functional Groups - AlkynesC≡C is the alkyne functional group, also known as

a carbon-carbon triple bond.

line angle structureLewis 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.

line angle structureLewis structure

2-bromopropane or propyl bromide, CH3CHBrCH3

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.

line angle structuresLewis structure

benzene, C6H6

Aromatic Hydrocarbons

contain 6-membered 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

alkyne

halide

- X

aromatic ring

Functional Groups - AlcoholsAlcohols all have the –OH group (called a

hydroxyl group and sometimes shown as HO-).

line angle structureLewis structure

Isopropyl alcohol or 2-propanol, CH3CHOHCH3

Ethers

• are like water, with alkyl groups replacing both of the -Hs: H-O-H water R-O-H alcohol R-O-R’ 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 (CH3)3N ethylamine trimethylamine

pyrrolidine

All three functional groups in blue are amines.

Functional Groups

alcohol

amine (1°)

ether

R = alkyl group, which isa group containing C’s and H’s with no multiple bonds.

Some Aldehydes and Ketones O ║ R-C-R' ketone O ║ R-CH aldehyde

O O O O ║ ║ ║ ║HCH CH3CH CH3-CH2-CH CH3-C-CH3methanal ethanal propanal propanone(formaldehyde) (acetaldehyde) (acetone)

C=O is called a carbonyl group

Functional Groups - Carboxylic Acids

Carboxylic acids (-COOH) are organic acids.

line angle structure

Lewis structure

lauric acid, CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2COOH

Note that the -OH group and the =O are on the same C atom.

Functional Groups - EstersThe fats in our bodies are esters. Below is a

simple ester.

line angle structureLewis structure

ethyl acetate, CH3CO2CH2CH3

The ester group is in green.Although carbon and most hydrogen atoms aren’t shown, other atoms are.

Functional GroupsAmines, Amides, and Nitriles

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.

amines

amides

Functional Groups

aldehyde

ketone

carboxylic acid

ester

amide

nitrile

- C≡N

Functional GroupsCircle and label each functional group.

vitamin A (retinol)

aspirin

alcohol

alkenes (5)

ester

carboxyl group

aromatic ring…NOT three alkenes!

Functional GroupsCircle and label each functional group.

estrogen

All -OH are alcohols. Note that some are written HO-.

aromatic ring

a triglyceride

alkenes (4), all cis

ester (3)

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

CH3 CH2 CH2CH2COOH

Now, draw the 3-D structure for this compound.

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

Molecularformula Condensed Structural Formula NameCH4 CH4 methane

C2H6 CH3CH3 ethane

C3H8 CH3CH2CH3 propane

C4H10 CH3CH2CH2CH3 butane

C5H12 CH3CH2CH2CH2CH3 pentane

C6H14 CH3CH2CH2CH2CH2CH3 hexane

C7H16 CH3CH2CH2CH2CH2CH2CH3 heptane

C8H18 CH3CH2CH2CH2CH2CH2CH2CH3 octane

C9H20 CH3CH2CH2CH2CH2CH2CH2CH2CH3 nonane

C10H22 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 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.

stereo-isomerism

substituents

main chain

unsaturation functional group

Nomenclature of Alkanes1. 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.

CH3 - CH - CH3

|

CH3 - CH - CH2

|

CH3

54

3

21

Nomenclature of Alkanes

3. Name and give the location of each substituent group.

Condensed Structural Formula Name

CH3— methyl

CH3CH2 — ethyl

CH3CH2CH2 — propyl

CH3CH2CH2CH2 — butyl

CH3CH2CH2CH2CH2 — pentyl

(CH3)2CH — isopropyl

(CH3)3C— t-butyl

Nomenclature of Alkanes

4. When two or more substituents are present, list them in alphabetical order.

Condensed Structural Formula Name

CH3— methyl

CH3CH2 — ethyl

CH3CH2CH2 — propyl

CH3CH2CH2CH2 — butyl

CH3CH2CH2CH2CH2 — pentyl

(CH3)2CH — isopropyl

(CH3)3C— t-butyl

Nomenclature of Alkanes

2,4-dimethylpentane

CH3 - CH - CH3

|

CH3 - CH - CH2

|

CH3

54

3

21

CH3

|

CH3 - CH - CH2

|

CH - CH - CH2 - CH3

| |

CH3 CH - CH3

|

CH3

3-ethyl-2,4,5-trimethylheptane

5

43

2

1

6

7

Drawing an Alkane from its Name

CH2 - CH3

|

CH3 - CH - CH - CH2 - CH3

|

CH3

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.

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.