Organic for Chem II

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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!**

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You must correctly show

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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

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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 , CH 4 formaldehyde , CH 2 O acetonitrile , CH 3 CN

Carbon

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Bond lengths: C —C > C=C > C≡C

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Bond strengths: C≡C > C=C > C—C

Carbon

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Hydrocarbons containing no multiple bonds are not very reactive.

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Organic compounds get their reactivity and their characteristics from functional groups such as -OH (alcohol) and -COOH (acid).

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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 formula C 6 H 12 hexane, a straight chain alkane formula C 6 H 14

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, CH 3 CHBrCH 3 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!

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.

It is a unique structure

Lewis structure line angle structures benzene, C 6 H 6

Aromatic Hydrocarbons

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contain 6 membered ring structures with alternating double bonds, stabilized by the delocalized electrons from the pi bonds.

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are not as reactive as the alkenes and alkynes.

alkene

Functional Groups

- 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, CH 3 CHOHCH 3 Lewis structure line angle structure

Ethers

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are like water, with alkyl groups replacing both of the -H s:

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H -O H R-O R-O H R’ water alcohol ether

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are relatively unreactive.

are commonly used as solvents.

Functional Groups - Amines

Amines are organic bases and have the formula RNH 2 , RNR’R”, or RNHR’ , where R is an alkyl group.

CH 3 CH 2 NH 2 ethylamine (CH 3 ) 3 N 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 ketone aldehyde C=O is called a carbonyl group O ║ HCH

methanal (formaldehyde)

O ║ O ║ O ║ CH 3 CH

ethanal (acetaldehyde)

CH 3 -CH 2 -CH CH 3 -C-CH 3

propanal propanone (acetone)

Functional Groups Carboxylic Acids

Carboxylic acids (-COOH) are organic acids.

lauric acid, CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 COOH 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, CH 3 CO 2 CH 2 CH 3 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

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Amides are like amines, but with an adjacent C=O.

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Be careful! Both amines and amides have different forms: primary (1 °), secondary (2°), and tertiary (3°).

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Nitriles are R-CN.

Functional Groups

aldehyde ketone carboxylic acid amide

- C ≡N

nitrile ester

Functional Groups

Circle and label each functional group.

alcohol alkenes (5) vitamin A (retinol) carboxyl group aromatic ring…NOT three alkenes!

aspirin ester

Functional Groups

Circle and label each functional group.

ester (3) a triglyceride alkenes (4), all cis aromatic ring All -OH are alcohols. Note that some are written HO-.

estrogen

3-D Structure

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Solid lines are bonds in the plane of the board or paper.

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Wedges show bonds to atoms in front of the plane.

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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

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

Start practicing now

3-Drawing Structure

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

CH 3 CH 2 CH 2 CH 2 COOH

Nomenclature

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Organic compounds get their reactivity and their characteristics from functional groups.

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Organic compounds are named after the functional groups they contain.

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We will start with the alkanes.

Alkanes

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are characterized by stable C-C single bonds

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are aka saturated hydrocarbons.

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are named for the number of carbons in the longest chain.

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have no functional groups.

Alkanes

Molecular formula CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 5 H 12 C 6 H 14 C 7 H 16 C 8 H 18 C 9 H 20 C 10 H 22 Condensed Structural Formula CH 4 CH 3 CH 3 CH 3 CH 2 CH 3 CH 3 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Name methane ethane propane butane pentane hexane heptane octane nonane decane

Nomenclature

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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 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 5 1 CH 3 - CH - CH 3 | 2 CH 3 - CH - CH 2 | 3 CH 3

Nomenclature of Alkanes

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

Condensed Structural Formula Name CH 3 — CH 3 CH 2 — CH 3 CH 2 CH 2 — CH 3 CH 2 CH 2 CH 2 — CH 3 CH 2 CH 2 CH 2 CH 2 — (CH 3 ) 2 CH (CH 3 ) 3 C — — methyl ethyl propyl butyl pentyl isopropyl t-butyl

Nomenclature of Alkanes

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

Nomenclature of Alkanes

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.

CH 2 | - CH 3 CH 3 - CH - CH - CH 2 - CH 3 | CH 3

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, CH 3 CHO

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.