C30 Organic part 1

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Chemistry 30 – Organic

Chemistry – Part 1

To accompany

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Organic Chemistry – Preparation – VSEPR

• Recall VSEPR Theory (valence shell electron pair repulson theory) from Chemistry 20

• Organic chemistry will involve 3 particular groupings:

• 0 lone pairs, 4 bonding pairs - tetrahedral

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Organic Chemistry – Preparation - VSEPR

• 0 lone pairs, 3 bonding pairs – trigonal planar

• 0 lone pairs, 2 bonding pairs - linear

O C O•• _•• _•• ••

•• •• ••••

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Organic Chemistry - Preparation

• Recall polarity of covalent bonds from Chemistry 20:

2 particular polar bonds important in organic chemistry

• C – H bonds are virtually non-polar

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Organic Chemistry – Preparation – Intermolecular Forces

• London Dispersion Forces – all

moleculars – temporary dipoles –

affected by total # of e- and shape

• Dipole-dipole Forces – polar moleculars

• Hydrogen Bonding (H covalently bonded to F, O, or N)

affect melting

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Organic Chemistry – 14.1 - Introduction

• Organic compounds – originally defined to be compounds from living or once-living organisms

• Wohler, 1828, synthesized urea (an organic compound) from inorganic chemicals

• Today organic compounds defined to be

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• Most existing compounds are organic!

• Special things about carbon that allow it to form so many different compounds:

• 4 bonding electrons

• ability to form single, double, triple bonds with itself

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• Classification:

organic compounds

hydrocarbons C and H only

hydrocarbon derivatives

C and H along with O, N, and/or halogen atoms

aliphatics

without aromaticswith

alkynes – 1 triple bond between C’s – C_nH_2n-2

alkenes – 1 double bond between C’s – C_nH_2n

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Organic Chemistry – 14.2 - Hydrocarbons

• Alkanes - saturated hydrocarbons

• Term saturated used because alkanes have the maximum number of hydrogens

• General formula: C_nH_2n+2

butane

first 4 alkanes

methane ethane

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• The unbranched alkanes are a homologous series because they differ by the number of CH₂units in each

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• Since carbons and

hydrogens can join up in so many ways, structural

formulas are used • Different types

of structural formulas:

3

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Organic Chemistry – 14.2 – Hydrocarbons: Alkanes

• Nomenclature of alkanes:

• You must learn the following prefixes: _{# of C’s} _prefix

1 meth

2 eth

3 prop

4 but

5 pent

6 hex

7 hept

8 oct

9 non

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• Start naming by finding the longest continuous chain of carbon atoms. Name the long chain

using its prefix with an ane ending.

• Identify branches, and name using their prefix with a yl ending.

• Number the longest continuous chain from the

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• These rules will be introduced by the following examples

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Example 1:

CH₃ – CH – CH – CH₂ – CH₂ – CH₃ CH₃

CH₂- CH₃

CH₃ – CH – CH – CH₂ – CH₂ – CH₃ Root name: hexane

CH₃

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Example 1:

CH₃ – CH – CH – CH₂ – CH₂ – CH₃ CH₃

CH₂- CH₃

CH₃ – CH – CH – CH₂ – CH₂ – CH₃ Root name: hexane

CH₃

CH₂- CH₃

Identify side groups

ethyl methyl

number carbon chain to locate branches

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• Compound name:

3-ethyl-2-methylhexane

long chain side group _{side group}

position on long chain

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CH₃ – CH – CH – CH – CH₃ CH₃

CH₃ CH₃

CH₃ – CH – CH – CH – CH₃

CH₃

CH₃ CH₃

CH₃ – CH – CH – CH – CH₃ CH₃

CH₃ CH₃

CH₃ – CH – CH – CH – CH₃

CH₃

CH₃ CH₃

CH₃ – CH – CH – CH – CH₃ CH₃

CH₃ CH₃

Example:

No matter how the long chain is selected, the name is the same: 2, 3, 4 - trimethylpentane

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• Example:

CH₃ – CH₂ – C – CH₃ CH₂ – CH₃

CH – CH₃

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CH₃ – CH₂ – C – CH₃ CH₂ – CH₃

CH – CH₃

CH₂ – CH₃

3 – ethyl – 3, 4 – dimethylhexane or 4 – ethyl – 3, 4 - dimethylhexane

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• Doing the reverse process is actually easier – draw your long chain and attach the groups in the

addressed spots

• Start by drawing the long chain without any hydrogens – don’t worry about orientation • Add side groups in their addressed spots • Add hydrogens (each C gets 4 bonds)

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• Physical Properties of Alkanes: • All alkanes are non-polar,

only intermolecular forces = London Dispersion Forces – boiling point and melting point

increase with number of carbons (see chart page 551) KNOW

all alkanes are insoluble in water

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Organic Chemistry – 14.2 – Hydrocarbons: Alkenes

• Alkenes are hydrocarbons with 1 double bond

• Note dienes and trienes also exist – we’ll focus on

compounds with 1 double bond

• Alkenes with 1 double bond have the general

formula, C_nH_2n

• Since they have 2 less hydrogens than corresponding

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• Alkene formulas:

• Alkenes are trigonal planar around the doubly bonded C’s and tetrahedral around the others

3

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• Nomenclature of alkenes:

find longest continuous chain of carbons that

contains the double bond – same prefixes as for alkanes

add ene to the prefix along with a number to indicate the position of the double bond (for ethene and propene a position number is not needed)

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• Example:

CH₃ – CH₂ – CH₂ – C = CH₂ CH₂ CH₃

CH₃ – CH₂ – CH₂ – C = CH₂

CH₂

CH₃ 2 – ethylpent-1-ene

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• Physical properties of alkenes:

• Like alkanes, alkenes are non-polar and are

insoluble in water

• Boiling points are slightly lower than those for alkanes with the same number of carbons

Why?

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Organic Chemistry – 14.2 – Hydrocarbons: Alkynes

• Alkynes are unsaturated hydrocarbons with 1 triple bond

• General formula C_nH_2n-2

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• Alkynes are non-polar aliphatic hydrocarbons like alkanes and alkenes

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• Note that alkynes have higher boiling points than alkanes or alkenes

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• Accepted explanation is that for short chain

alkynes, the linear structure around triple bond

allows them to come closer together than

alkanes or alkenes with same number of

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• Nomenclature of alkynes is identical to that of alkenes, the only exception is the ending:

yne, not ene

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Organic Chemistry – 14.2 – Hydrocarbons: Cyclics

• Cyclic analogues exist for alkanes, alkenes, and alkynes

• General formulas will contain 2 less hydrogens than the open chain hydrocarbons:

cycloalkanes C_nH_2n, cycloalkenes C_nH_2n-2, cycloalkynes C_nH_2n-4

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• Line structures are commonly used for the ring part of cyclic hydrocarbons

• Always draw them this way

• Examples:

CH₂

CH₂ CH₂

cyclopropane:

not CH2

CH₂

CH

not

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• Cyclics will always have names ending with cyclo_____ane or cyclo_____ene

• Don’t worry about cyclo_____ynes, you will not encounter them

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CH₂ – CH₃ _{ethylcyclopentane}

No numbers needed. Why?

CH₂ – CH₃ _{3-ethylcyclopentene} Always start at far side of

double bond and number clockwise or counter-clockwise towards group

CH₂ – CH₃

CH₃

4-ethyl-3-methlycyclpentene _{As above. This one must be} numbered counter-clockwise to give lowest set of

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CH₂ – CH₃

CH₃ 1-ethyl-2-methylcyclopentane This time the numbering is clockwise since double bond isn’t a factor and when possible lowest

number goes on first group

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Organic Chemistry – 14.2 – Hydrocarbons: Aromatics

• Aromatics: all contain the grouping

• Originally this grouping thought to be:

• Problems: • all bonds found to be equal length

• this compound should be very reactive

but is actually very stable

6 6

C H_

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• Today we believe it to be made up of bonds that are neither single nor double but a hybrid of both

• We draw the structure

• Its name is benzene

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• Nomenclature of Aromatics:

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• Examples:

CH₃

CH₂ – CH₃

CH₂ – CH₂ – CH₃

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Organic Chemistry – 14.3 – Hydrocarbon Derivatives

hydrocarbon derivatives

C and H along with O, N, and/or halogen atoms

alkanes – all single bonds – C_nH_2n+2

organic compounds

hydrocarbons C and H only

aliphatics

without aromaticswith

alkynes – 1 triple bond between C’s – C_nH_2n-2

alkenes – 1 double bond between C’s – C_nH_2n

alcohols R-OH akyl halides R-X carboxylic acids R-C-OH= O esters

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• Hydrocarbon derivatives contain other elements besides C and H; most commonly O, N, or

halogen atom

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Organic Chemistry – 14.3 – Hydrocarbon Derivatives: Alcohols

• Alcohols – functional group: “-OH” hydroxyl group

• Common alcohols: table 14.7, page 566

3

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• Nomenclature of alcohols

• Key points – long chain must have “–OH” attached to it

• Numbering of the long chain starts from the end closest to “-OH”

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CH₃ – CH₂ – CH₂

CH₃ – CH – CH₂ – CH₂ – OH

CH₃ – CH₂ – CH₂

CH₃ – CH – CH₂ – CH₂ – OH _{3-methylhexan-1-ol}

side group

position of side group

position of OH

length of long chain containing OH*

* don’t count OH in length of chain

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• Example

CH₂ – CH – CH₂ OH

OH

CH₂ – CH – CH₂

OH

propane - 1, 2, 3 - triol

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• Physical properties of alcohols

• Because of the hydrogen bonding between OH

groups in adjacent molecules,

• alcohols have much higher boiling points than

hydrocarbons (1-12 C’s are liquids at SATP)

• small alcohols are totally miscible with

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Organic Chemistry – 14.3 – Hydrocarbon Derivatives: Alkyl Halides

• Alkyl halides contain at least 1 halogen atom, (F, Cl, Br, I)

• Alkyl halides are all synthetic compounds

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• Nomenclature of alkyl halides:

long chain must be attached to halogen atom(s)

identical to nomenclature of hydrocarbons

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• Example:

CH₃ – CH₂ – CH – CH – CH – CH₃ Br

Cl

Br

CH₃ – CH₂ – CH – CH – CH – CH₃

Br

Cl

Br

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• Do Practice Problems 31, 32, page 569

Br

Cl

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Organic Chemistry – 14.3 – Hydrocarbon Derivatives: Carboxylic Acids

• Carboxylic acids are weak organic acids containing the carboxyl functional group,

often written –COOH

• When carboxylic acids, ionize, the process is:

- C – OH , = O

R - C – OH , = O

R - C – OH(aq) = O

R - C – O= -(aq)

O H+(aq) +

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• Common carboxylic acids, acetic acid (active ingredient of vinegar) and citric acid

• Nomenclature of carboxylic acids:

In all carboxylic acids the carboxyl group is at one end of the molecule

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• Example:

CH₃ – C – CH₂ – CH₂ – C – OH= O

CH₂ CH₃ CH₃

CH₃ – C – CH₂ – CH₂ – C – OH= O

CH₂ CH₃

CH₃

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• Physical properties of carboxylic acids:

• Like alcohols they have hydrogen bonding, but

hydrogen bonding at 2 sites, -C=O and –OH

• This leads to higher boiling points and greater solubility than alcohols with same number of C’s

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Organic Chemistry – 14.3 – Hydrocarbon Derivatives: Esters

• Esters have the general formula:

often written RCOOR′

• Esters are formed from the reaction of an

alcohol and a carboxylic acid; the formation or esterification reaction is the key to naming them

R(or H) - C – O – R= ′

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R - C – O - H =

O

+ H - O - R′ R - C – = O - R′

O

+ HOH

carboxylic

acid alcohol ester water

It’s important that when you look at ester, that you’re able to recognize part that came from alcohol and part that came from acid

Acid part contains C; alcohol part is bonded directly to O

O

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• General form of name: _______yl _________oate

from

alcohol

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• Examples:

CH₃ – CH₂ – C – O – CH= ₃ O alcohol part: methyl acid part: propanoate methyl propanoate

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Organic Chemistry – 14.4 – Refining and Using Organic Compounds

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• Physical properties of esters:

• fruity odour in some cases

• polar but lack of OH bond means no hydrogen bonding, so lower boiling points than alcohols and carboxylic acids

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• Petroleum: mixture of hydrocarbons (primarily alkanes and alkenes) found in natural gas,

crude oil, and bitumen (from tar sands)

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• Fractional

distillation: a means of

separating petroleum components based on

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• Read and discuss page 578 regarding fractional distillation

• Fractional distillation is a physical process; mixture is separated into

fragments with a small range of boiling

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• Next stages of petroleum refining are chemical processes:

• cracking – breaks carbon-carbon bonds • reforming – forms carbon-carbon bonds

alkylation (special case of reforming) forms 2,2,4-trimethylpentane from smaller hydrocarbons

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