introduction to organic chemistry:...

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Introduction to Organic Chemistry:

Hydrocarbons

Chapter 12


Chapter 12

12.1 – Organic Compounds

12.2 – Alkanes

12.3 – Alkanes with Substituents

12.4 – Properties of Alkanes

12.5 – Alkenes and Alkynes

12.6 – Cis-Trans Isomers

12.7 – Addition Reactions for Alkenes

12.8 – Aromatic Compounds

12.1 – Organic CompoundsIdentify properties characteristic of organic or inorganic compounds.

Organic Compounds

Organic chemistry is the study of carbon compounds.

An organic compound

• Always contains carbon and hydrogen atoms

• May also contain other nonmetals such as oxygen, nitrogen, phosphorus, or a halogen.

• Organic compounds are found in:

• Gasoline, medicines, shampoos, plastics, and perfumes

• Carbohydrates, fats, and proteins

Functional Groups

• Organic compounds are organized by their functional groups (groups of atoms bonded in a specific way).

• Compounds that contain the same functional groups have similar physical and chemical properties.

• The identification of functional groups allows us to classify organiccompounds according to their structure, to name compounds within each family, and to predict their chemical reactions.


Organic vs. Inorganic

• In chemistry, molecules are classified as Organic or

Inorganic.

• Inorganic compounds are (quite expansively)

anything that is not organic.

• Organic and Inorganic compounds have different

properties.

– Organic compounds:

▪ Have low melting and boiling points.

▪ Are flammable and undergo combustion.

▪ Are not soluble in water.

– Inorganic compounds

▪ Many inorganic compounds have high

melting and boiling points.

▪ Inorganic compounds that are ionic are

usually soluble in water, and most do not

burn in air.


Practice

Identify each characteristic as most typical of compounds that are inorganic or organic.

A. It has a high melting point.

B. It is not soluble in water.

C. It contains carbon and hydrogen atoms.

D. It has the formula MgCl2.

E. It burns easily in air.


Representations of Carbon Compounds

• Hydrocarbons are organic compounds that consist of only carbon and

hydrogen.

– In organic molecules, every carbon atom has four bonds.

– In methane (CH4), the carbon atom forms an octet by sharing its four

valence electrons with four hydrogen atoms.

Three-dimensional and two-dimensional representations of methane: a)

space-filling model, b) ball-and-stick model, c) wedge-dash model, d)

expanded structural formula, and e) condensed structural formula


Representations of Carbon Compounds

• In ethane (C2H6), each tetrahedral carbon forms three covalent bonds to

hydrogen and one to the other carbon.


Alkanes

Alkanes

• are formed by a continuous chain of carbon atoms.

• are named using the IUPAC (International Union of Pure

and Applied Chemistry) system.

• have names that end in ane.

• use Greek prefixes to name carbon chains with five or

more carbon atoms.


Study Check

In the butane molecule (C4H10), predict the shape around

each carbon atom.

C

H

H

H C

H

H

C

H

H

C

H

H

H


Chapter 12


12.2 – Alkanes








12.2 - AlkanesWrite the IUPAC names and draw the condensed or line-angle structural

formulas for alkanes and cycloalkanes.


Alkanes

• More than 90% of the compounds in

the world are organic compounds.

• The larger number of carbon

compounds is possible because the

covalent bonds between carbon

atoms (C-C) is very strong, allowing

carbon atoms to form long, stable

chains.


Alkanes

• The alkanes are a type of hydrocarbon in which the carbon atoms are

connected only by single bonds.

– Alkanes are formed by a continuous chain of carbon atoms.

– The names of alkanes and in –ane.

▪ Such names are part of the IUPAC system (International Union

of Pure and Applied Chemistry) used by chemists to name

organic chemistry.

– Alkanes made of carbon chains are named based on how many

carbons make up the chain.

– One of the most common uses of alkanes is as fuels.

▪ Methane, propane, octane, and hexane are all alkanes used

as fuels.


IUPAC Names of Alkanes


Line-Angle Structural Formulas

A simplified structure of organic molecules

• is called the line-angle structural formula.

• shows a zigzag line in which carbon atoms are

represented as the ends of each line and as corners.

Carbon atoms

• at the end are bonded to three hydrogen atoms.

• in the middle are bonded to two hydrogen atoms.


Condensed formula and Line-angle formula

• Pentane


Condensed formula and Line-angle formula

• Draw the condensed structural formula and name the molecule:


Guide to Drawing Structural Formulas for

Alkanes

Step 1: Draw the carbon chain.

Step 2: Draw the expanded structural formula by adding the

hydrogen atoms using single bonds to each of the

carbon atoms.

Step 3: Draw the condensed structural formula by combining

the H atoms with each C atom.

Step 4: Draw the line-angle structural formula as a zigzag

line in which the ends and corners represent C

atoms.


Drawing Expanded, Condensed, and Line-

Angle Structural Formulas (1 of 3)

Draw the expanded, condensed, and line-angle structural

formula for pentane.

Step 1: Draw the carbon chain. A molecule of pentane has

five carbon atoms in a continuous chain.

Step 2: Draw the expanded structural formula by adding

the hydrogen atoms, using single bonds to each

of the carbon atoms.






Step 3: Draw the condensed structural formula by

combining the H atoms with each C atom.






Step 4: Draw the line-angle structural formula as a

zigzag line in which the ends and corners

represent C atoms.


Conformations of Alkanes

• Single bonds can spin and rotate.

• Thus different arrangements, known as conformations, occur during

the rotation about a single bond.

• http://symmetry.otterbein.edu/gallery/index.html


Structural Formulas: C4H10

As butane (C4H10) rotates, sometimes the

line up in front of each other, and at other times they are

opposite each other. Butane can be drawn using a variety of

two-dimensional condensed structural formulas:


Structural Formulas: C4H10


Cycloalkanes

Hydrocarbons can also form into circles or rings called:

cycloalkanes

• have two fewer hydrogen atoms than the open chain form.

• are named by using the prefix cyclo before the name of

the alkane chain with the same number of carbon atoms.


Formulas of Cycloalkanes

Table 12.4 Formulas of Some Common Cycloalkanes

Name BLANK BLANK BLANK

Cyclopropane Cyclobutane Cyclopentane Cyclohexane

Ball-and-Stick Model BLANK BLANK BLANK

Three carbons single-bonded to each other in a triangular pattern,

with each carbon single-bonded to 2 hydrogens.

The ball and stick model shows four

carbons single-bonded to each other in a

square pattern, with each carbon single-

bonded to 2 hydrogens.

The ball and stick model shows five

carbons single-bonded to each other in

a pentagonal pattern, with each carbon

single-bonded to 2 hydrogens.

The ball and stick model shows six

carbons single-bonded to each other in

a hexagonal pattern, with each carbon

single-bonded to 2 hydrogens.

Condensed Structural Formula BLANK BLANK BLANK

The condensed structural formula shows a triangular ring of three C

H 2 molecules.

The condensed structural formula shows

a square ring of four C H 2 molecules.

The condensed structural formula

shows a pentagonal ring of five C H 2

molecules.

The condensed structural formula

shows a hexagonal ring of six C H 2

molecules.

Line-Angle Structural Formula BLANK BLANK BLANK

The line-angle structural formula is a triangle. The line-angle structural formula shows a

square.

The line-angle structural formula shows

a pentagon. The line-angle structural formula shows

a hexagon.


Study Check

Give the IUPAC name for each of the following compounds:

A.

B.


Study Check

Name the following alkanes:

A.

B.

C.

D.


Chapter 12


12.2 – Alkanes








12.3 – Alkanes and Substituents

Write the IUPAC names for alkanes with substituents and draw their

condensed and line-angle structural formulas.


Structural Isomers

Structural isomers

• have the same molecular formula with a different arrangement

of atoms.

• have the same number of atoms bonded in a different order.

Butane (C4H10) has two structural isomers: a straight chain and a

branched chain.


Study Check

Draw three possible structural isomers of pentane

(C5H12).


Solution

Draw three possible structural isomers of pentane

(C5H12).

Structural

Isomers of

C5H12

Structural Isomers of C5H12 Structural Isomers of

C5H12

Structural Isomers

of C5H12

CondensedThe first condensed structural formula is a straight chain of single-bonded molecules as follows. C H 3, C H 2, C H 2, C H 2, C H 3. The second condensed structural formula is a branched chain as follows. C H 3, C H single-bonded to C H 3 above,

C H 2, C H 3.The third condensed structural formula is a central C

single-bonded to four C H 3 molecules above, below,

rightward, and leftward.

Line-AngleThe line-angle structural formula shows a zigzag line made of 4 segments forming 3 angles. The line-angle structural formula shows a zigzag of 3 segments forming 2 angles, with

a fourth segment rising vertically from the first angle.

The line-angle structural formula shows 2 rising and falling line

segments with 2 segments rising diagonally right and left from the angle.


Study Check

Is the pair of formulas structural isomers? Or the same molecule?


Substituents in Alkanes

• When CH3 branches off of a carbon chain, it’s called an alkyl group

• When a halogen atom (Group 17) is attached to a carbon chain, it is

named as a halo group with the terms –fluoro, -chloro, -bromo, -iodo

based on which element it is.


Substituents and Alkyl Groups

Table 12.5 Formulas and Names of Some Common Substituents

Formula

Name

Formula, C H 3, single bond. name, methyl.

Formula, straight chain, C H 3, C H 2, single

bond. name, ethyl.

BLANK BLANK

Formula

Name

Formula, straight chain, C H 3, C H 2, C H 2, single bond. name,

propyl.

Formula, branched chain, C H 3, C H with single bond above, C

H 3. name, isopropyl. BLANK BLANK

Formula

Name

Formula, straight chain, C H 3, C H 2, C H 2, C H 2, single bond.

name, butyl.

Formula, branched chain, C H 3, C H single-bonded to C H 3

above, C H 2, single bond. name, isobutyl.

Formula, C H 3, C H with single bond above, C H 2,

C H 3. name, secondary butyl.Formula, central C with single bond

above and three C H 3 molecules

below, rightward, and leftward.

name, tertiary butyl.

Formula

Name

Formula, F, single bond. name, fluoro. Formula, F, single bond. name, fluoro. Formula, B r, single bond. name, bromo. Formula, I, single bond. name, iodo.


Naming Alkanes with Substituents


Naming Cycloalkanes with Substituents


Naming Haloalkanes

Haloalkanes

• are alakanes with a halogen atom that replaces a hydrogen atom.

• are named by putting the substituents in alphabetical order.

• have the halo group numbered according to the carbon where it is

attached to the alkane.

Examples of

Haloalkanes

BLANK BLANK BLANK BLANK

Formulastraight chain, C H 3, C l straight chain, C H 3, C H 2, B r Branched chain, C H 3, C H single-bonded to an F above A central C single-bonded to C l above and three C H 3 molecules below, rightward, and leftward

IUPAC Chloromethane Bromoethane 2-Fluoropropane 2-Chloro-2-

methylpropane

Common Methyl chloride Ethyl bromide Isopropyl fluoride Tert-Butyl chloride


Drawing the molecule from the name

Draw the condensed and line-angle structural formulas for

2,3-dimethylbutane.


Drawing the molecule from the name

Draw the condensed and line-angle structural formulas for

2-bromo-3-ethyl-4-methylpentane.


Chapter 12


12.2 – Alkanes









Identify the properties of alkanes and write a balanced chemical

equation for combustion.


Properties of Alkanes

Many types of alkanes are the components

of fuels that power our cars and oil that

heats our home.

The solid alkanes that make up waxy

coatings on fruits and vegetables help

retain moisture, inhibit mold, and enhance

appearance.

The different uses of alkane compounds

result from their physical properties,

including their solubility and density.


Uses of Alkanes (1 of 2)

Alkanes with one to four carbons are gases at room

temperature and are widely used as heating fuels.

methane, ethane, propane, butane

Butane has four carbons:

Alkanes with five to eight carbons are highly volatile liquids

at room temperature, which makes them useful as fuels.

pentane, hexane, heptane, octane

Octane has eight carbons:


Uses of Alkanes (2 of 2)

Alkanes with 9−17 carbons are liquids with higher boiling

points and are found in motor oils, mineral oil, kerosene,

diesel, and jet fuels.

Decane has 10 carbons:

• Alkanes with 18 or more carbon atoms, known as

paraffins, are waxy solids at room temperature.

• Petroleum jelly, or Vaseline, is a semisolid mixture of

hydrocarbons with more than 25 carbon atoms.


Melting and Boiling Points (1 of 4)

Alkanes

• have the lowest melting and boiling points of organic

compounds.

• contain only the nonpolar bonds of

• exhibit only weak dispersion forces in the solid and liquid states.

Longer-chain alkanes have more dispersion forces.



Branched alkanes

• have lower boiling points than the straight-chain isomers.



Branched alkanes

• have lower boiling points than the straight-chain isomers.

• tend to be more compact, reducing the points of contact

between the molecules.

• do not have linear shapes and cannot line up close to each

other.



Cycloalkanes

• have higher boiling points than the straight-chain alkanes

with the same number of carbon atoms.

• have limited rotation of carbon bonds; they maintain their

rigid structure and can be stacked closely together, which

gives them many points of contact and attractions to each

other.



We can compare the boiling points of straight-chain alkanes,

branched-chain alkanes, and cycloalkanes.Table 12.6 Comparison of Boiling Points of Alkanes and Cycloalkanes with Five Carbons

Formula Name Boiling Point (°C)

Straight-Chain Alkane BLANK BLANKStraight chain alkanes. condensed structural formula, C H 3, C H 2, C H 2, C H 2, C H 3

Pentane 36

Branched-Chain Alkanes BLANK BLANKBranched chain alkanes. condensed structural formula, C H 3, C H single-bonded to C H 3, C H 2, C H 3

2-Methylbutane 28

Central C single-bonded to four C H 3 molecules

Dimethylpropane 10

Cycloalkane BLANK BLANKline-angle structural formula, a pentagonal ring

Cyclopentane 49


Combustion of Alkanes (1 of 3)

The carbon–carbon single bonds in alkanes are difficult to

break, which makes them the least reactive family of organic

compounds.

However, alkanes burn readily in oxygen to produce carbon

dioxide, water, and energy.

Alkane O2 CO2 H2O + energyg g g g


Combustion of Alkanes (3 of 3)

Methane is the natural gas we use to cook our food and

heat our homes. The equation for the combustion of

methane (CH4) is written as follows:

4 2 2 2CH 2O CO 2H O + energyg g g g

Propane is the gas used in portable heaters and gas

barbecues. The equation for the combustion of propane

(C3H8) is written as follows:

4 2 2 2CH 5O 3CO 4H O + energyg g g g


Solubility and Density of Alkanes

Alkanes are

• nonpolar.

• insoluble in water.

• less dense than water.

• flammable in air.

• found in crude oil.

If there is an oil spill in the ocean, the alkanes in the crude oil

do not mix with the water but float on top, forming a thin

layer on the surface.


Chapter 12


12.2 – Alkanes







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