✩1- Introduction to Alkanes

Introduction to Organic Chemistry/ Alkanes

Part 1 - Carbon - Recap

Why can carbon form so many compounds?

What we know about carbon

• 1s22s22p2

• Four valence electrons

• Non-metal

How many bonds can it form?

• 2, 3 or 4

What type of bonds can it form?

• Covalent

• Single or multiple

• What atoms can it bond to?

  • Many

  • Commonly other carbon, hydrogen, nitrogen, oxygen, sulfur, halogens

Part 2 - Hydrocarbons - Main Focus on Acyclic Alkanes and Alkenes

◻ Background Info:

Are the simplest organic molecules as they only contain hydrogen and carbon yet they vary in complexity and so are simplified by grouping.

◻NAMING HYDROCARBONS

Hydrocarbon use prefixes and suffices

Prefix → Number of carbons (Prop for 3 etc)

Suffix → Type of Hydrocarbon (“-ane” for alkanes, “-ene’ for alkenes)

◻ AKLANES

The simplest alkane contains one carbon

Alkanes are the simplest [hydrocarbon] because they only have single carbon-carbon (c-c) bonds. Alkanes contain the maximum possible number of atoms and are said to be saturated.

◽ Alkanes are saturated

• Breaking down the sentence:

  “maximum possible number of atoms” → This refers to the fact that each carbon atom in an alkane forms four single covalent bonds (either with hydrogen atoms or other carbon atoms). This configuration maximizes the number of hydrogen atoms attached to the carbon skeleton.

  “saturated” → In chemistry, when a molecule contains the maximum possible number of hydrogen atoms (with no double or triple bonds between carbon atoms), it is said to be "saturated." This term means that the molecule cannot accommodate any more hydrogen atoms without breaking the existing bonds.

So, putting it all together:

◽ Alkanes are saturated because

• Alkanes are hydrocarbons with only 4 single bonds (covalent)…

• Carbons in the alkanes are bonded to the maximum amount of atoms.

• Because of this, alkanes are said to be "saturated" with hydrogen.

◽Naming Alkanes

Prefix → number of carbons

Suffix → type of hydrocarbon ( -ane for alkanes)

• ◽Building the Alkane Series

  Be able to write

  • [x] Methane

  • [x] Ethane

  • [x] Propane

◽General Formula For Alkanes

CnH2n+2

◽Homologous Series

(Alkanes as a homologous series) where each successive member differs by a CH2 unit (a methylene group)

Info: Alkanes fall into a family that reacts similarly when interacting with other chemicals because of similar chemical properties

Homologous series: A group of organic compounds with similar general formula, chemical properties, and a graduation in physical properties where each successive series differs by a specific repeating unit.

Examples:

• Methane (CH₄): The simplest alkane, with one carbon atom.

• Ethane (C₂H₆): The next alkane, with two carbon atoms. It can be seen as methane plus one CH₂ unit.

• Propane (C₃H₈): Another alkane, with three carbon atoms. It can be seen as ethane plus one CH₂ unit.

• Butane (C₄H₁₀): Following the pattern, butane has four carbon atoms, which can be seen as propane plus one CH₂ unit.

✩2- Different Representations of Organic Compounds and Introduction

Different Representation of Organic Compounds and Intro to Structural Isomers

Learning outcomes

• [ ] To demonstrate how to represent alkanes using structural formulas, and semi-structural formulas.

• [ ] Identify the difference between a straight chain and a branched chain alkane

• [ ] Define what a structural isomer is.

◽REPRESENTING HYDROCARBONS

Drawing Semistructural Formuals for:

Ethane: CH3-CH3

Pentane: CH3-CH2-CH2-CH2-CH3

Heptane: CH3-CH2-CH2-CH2-CH2-CH2-CH3

◽ STRAIGHT CHAIN ALKANES VS BRANCHES CHAIN ALKANES

Straight Chain: All the carbons follow each other continuously

Branched Chain Alkanes: Not all the carbons follow each other continuously. (i.e there’s a parent chai and branched chain(s)

◽ STRUCTURAL ISOMERS

Structural isomers are molecules with the same molecular formula but different arrangements of their atoms

They have

• similar chemical properties

• different physical properties

• Straight-chain isomers tend to have higher boiling temperatures than branched chain isomers.

✩3- Isomers of Alkanes

Branching and isomers

learning outcomes:

• [x] Demonstrate the ability to name branched non-cyclic hydrocarbon compounds (up to C8) and structural isomers (up to C5) according to IUPAC systematic nomenclature.

• [x] Draw Structural Isomers of Alkanes

• C5 and C8 meaning

  "C8" and "C5": These notations refer to the number of carbon atoms in the hydrocarbon molecules. "C8" means a hydrocarbon with up to 8 carbon atoms, and "C5" means a hydrocarbon with up to 5 carbon atoms.

◻ NAMING STRUCTURAL ISOMERS OF ALKANES

Steps:

1. Identify the longest carbon chain + side chain

2. Number carbons from the end that give the side chain the lowest number possible

#Note: Naming side chains

Hydrocarbon side chains are called ‘alkyl’

Prefix is used to indicate the number of times a particular side chain appears

• Side chains of the SAME type are grouped and the position of each is shown (2,3-dimethylbutane)

• Side chains of DIFFERENT types are listed in alphabetical order (3-ethyl-2-methylpentane)

✩4-Alkanes

alkanes

learning outcomes:

• [ ] Name and draw Structural and Semi-Structural formula for Alkenes up to 8 carbon atoms

• [ ] Write the General formula for an alkene

• [ ] Identify that alkenes are unsaturated and be able to explain this term

• [ ] Name and draw branched chain alkenes

• [ ] Name and draw isomers for alkenes up to 5 carbon atoms

◻ ALKENES

They are hydrocarbons that contain one or more carbon-to-carbon double bonds.

Since each carbon atom is no longer bonded to the maximum possible number of atoms - alkenes are unsaturated hydrocarbons.

General Formula for alkenes: CNH2N

Naming alkenes

1. suffix “ene”

2. show the position of double bond

3. name carbons starting at end closet to the double bond

4. number of the first C that has double bonds is inserted between the prefix and suffix.

✩5-Functional Groups

functional groups

learning outcomes

• [ ] Be able to identify different functional groups, including, haloalkane, hydroxyl, and carboxyl groups and be able to name and draw molecules containing these.

FUNCTIONAL GROUPS

A functional group is an atom or group of atoms that has similar chemical properties when it occurs in different compounds. It defines the characteristic physical and chemical properties of families in an organic compound

#Note 1: slide 57

• Alkanes are not considered functional groups, instead a compound that lacks functional groups. However, the C-C double bond in carbons is considered a functional group.??

  Alkanes are not usually considered as functional groups; instead, an alkane is a compound that lacks functional groups. The C-C double bond in carbons, however, is considered a functional group.

HALOGENS

Has a carbon single bonded to a halogen (X=F,Cl,Br,I)

Use the prefix halo- (i.e. fluoro-, chloro-,bromo-, or iodo-)

(important to remember that the halogen is considered of equal rank with an alkyl group in the number of parent chains so the

• rule of side groups having to be numbered the lowest is applied

• if they are the same then which is alphabetically first is first)

HYDROXYL GROUP

Hydroxyl groups:

Molecules that contain a hydroxyl functional group are termed alcohols or alkanols

• contains OH

• uses the suffix “-ol” in naming (shows the position of the -OH using number before the suffix

hydroxyl groups take priority over halogens and alkyl groups

CARBOXYL GROUP

Molecules that contain a carboxyl group are termed carboxylic acids

• contain -C=O(OH)

• uses the suffix “-oic acid” (always on the final carbon in the chain)

carboxyl groups take priority over hydroxyl groups, halogens, and alkyl groups.

FUNCTIONAL GROUPS SUMMARY

A functional group is an atom or group of atoms with similar chemical properties in different compounds, defining the physical and chemical properties of families in an organic compound.

✩6- Properties of organic compounds

properties of organic compounds

learning outcomes

• [ ] To understand the physical properties of hydrocarbons.

• [ ] using their understanding of covalent bonding, polarity, and intermolecular forces.

• [ ] Explain what happens to mp and bp of branched-chain isomers vs straight chain isomers

• [ ] Identify the strongest intermolecular forces present in functional groups and use that to determine the link between melting and boiling points.

◻HOMOLOGOUS SERIES

Members of a homologous series have

• similar structure

• pattern to physical properties and similar chemical properties

• same general formula

Q: How does an increase in CH2 group change chemical and physical properties?

H: Intermolecular forces (hydrogen, dipole-dipole, dispersion forces) and chemical reactivity across single &double, triple bonds.

With increasing molecular mass both melting and boiling points increase while solubility in water tends to decrease

PHYSICAL PROPERTIES OF HYDROCARBON

PROPERTIES OF ALKANES: BOILING AND MELTING

As the molecular mass increases, the strength of dispersion forces increases because there are more opportunities for instantaneous dipoles to form with increasing molecular size

how does branching affect melting temperature

With a greater surface area for contact between molecules, the stronger the dispersion forces become. In general, the more branches that a molecule has, the smaller its area of contact with other molecules and therefore the weaker the dispersion force.

FACTOR THAT AFFECTS MELTING AND BOILING POINT

If comparing two straighter chained molecules of different sizes, the larger molecule (larger molecular mass) will have the higher melting/boiling point.

If comparing a straight-chain molecule with a branched molecule of similar size the straight-chain molecule will have a higher melting/boiling point.