Chemistry/Physical Setting Hydrocarbon Compounds Br. Jabreal

Aim: What conventions do chemists use to describe hydrocarbons? Do Now: What is meant by the term “organic”?

Organic Chemistry and Hydrocarbons Organic chemistry focuses primarily on compounds containing carbon *Organic compounds are compounds containing carbon By definition, compounds contain at least two different elements, so organic compounds must contain other elements bonded to the carbon hydrocarbons: Simplest organic compounds, containing only hydrogen and carbon.

Organic Chemistry and Hydrocarbons Because carbon has four valence electrons, it always forms _______ bonds, in order to complete its octet and become stable like a noble gas. It can form those four bonds in a variety of ways: in straight chains with four single bonds, combinations of single, double, or triple bonds, or even many times in a ring form

Examples of Hydrocarbons Ex. CH4 (Methane) Ex. C2H6 (Ethane) Ex. C2H4(Ethene)

Examples of Hydrocarbons Cyclohexane Benzene

Alkanes Alkane: hydrocarbon with only single covalent bonds. These are referred to as “saturated” hydrocarbons because they have only single bonds and contain the maximum number of hydrogen atoms a hydrocarbon can have. Follow general formula of CnH2n+2 n refers to number of carbon atoms in the compound. For example, if there is 1 carbon, there must be 2(1) + 2 = 4 hydrogens. Thus formula is CH4 Table Q of Reference Tables

Practice An alkane has four carbon atoms. Write the molecular formula for this alkane.

Structural Formula of Alkanes To draw the structural formula of an alkane: First draw in the straight chain of carbons, each connected to another carbon with a single bond. Then draw in the remaining bonds for each carbon, ensuring each carbon has four total bonds. The drawn in bonds should connect hydrogen atoms to the carbon. Ex. C4H10

Practice Draw the structural formula for C3H8. Draw the structural formula for an alkane with five carbon atoms.

Condensed Structural Formula Condensed Structural Formula: Simplified version of the structural formula without the dashed lines. Bonded carbons are simply written next to each other. Ex. Condensed Structural Formula: CH3CH2CH2CH3 Structural Formula

Alkenes and Alkynes Alkene: Hydrocarbon with at least one double bond. Follow general formula of CnH2n Ex. C2H4 Alkyne: Hydrocarbon with at least one triple bond. Follow general formula of CnH2n-2 Ex. C2H2

Alkenes and Alkynes *Alkenes and alkynes are considered unsaturated because they have double or triple carbon-carbon bonds. This makes the ratio of carbon to hydrogen less in these compounds.

Practice How many pairs of electrons are shared between two adjacent carbon atoms in a saturated hydrocarbon?

Practice Explain, in terms of chemical bonds, why the hydrocarbon is unsaturated.

Naming Alkanes, Alkenes, and Alkynes Alkanes, alkenes, and alkynes follow a two-part naming system The prefix of the name indicates how many carbon atoms are in the parental carbon chain. Refer to Table P for organic prefixes. Meth-: one, Eth-: two, Prop-: three, But-: four, Pent-: five, etc. The ending of the name indicates if its an alkane, alkene, or alkyne. Alkane: ends with –ane Alkene: ends with –ene Alkyne: ends with -yne

Naming Alkanes Example: CH4 There is only one carbon, so we must begin the name with the prefix “meth.” The formula follows the formula CnH2n+2, so it must be an alkane. The name must end in –ane. Therefore, the name is methane.

Naming Alkanes Example: Propane Prop: contains three carbon atoms ane: It’s an alkane. It must have all single bonds and follow CnH2n+2. Therefore, it has three carbons and 2(3) + 2 = 8 hydrogens. Thus, the formula of propane is C3H8.

Naming Alkenes Example: C4H8 It has four carbons, so it must use the prefix ______. Since it follows the general formula CnH2n, it must be an alkene. Therefore, the name must end with “ene”. Name: butene

Note: Naming Alkenes Note: the double bond in an alkene can be in different places. We state the location of the double bond with a #- before the name. Ex.

Review Which formula represents an alykne? CnHn C2nHn CnH2n+2 CnH2n-2

Review Polyvinyl chloride (PVC) is a polymer used to make drain pipes, flooring, electric wire, and some plastic bottles. Making PVC requires several reactions. The first step is represented by the equation below. Explain, in terms of chemical bonds, why the hydrocarbon in equation 1 is unsaturated.

Review What is the difference between 1-butene and 2-butene?

Naming Alkynes Example:

Practice Write the chemical formula, then draw the structural formula, of ethane. Write the chemical formula of pentane.

Practice Find the molecular formula, and then draw the structural formula for each of the following: 2-Pentene 1-butyne

Practice Name each of the following: C6H14 C2H4 C7H16 C5H8

Naming Alkanes: Branched-chain alkanes Sometimes alkanes are not just straight chains; they may have carbons branching out from the chain. In these cases, extra detail must be provided in the name. Ex.

Naming Alkanes: Branched-chain alkanes In cases where there are carbons branching from the alkane chain, two things must be identified: 1. The parental alkane chain This is identified as the longest carbon chain, although it is not necessarily in a straight line. 2. The substituent groups These are the groups or carbon chains branching off from the identified parental chain. If the carbon chain attached has only one carbon, it’s called “methyl.” If there are two carbons in the chain attached its called “ethyl.” For three “propyl.”

Naming Alkanes: Branched-chain alkanes We name the compound by stating the name of the parental chain, and adding the information about the substituent groups before the parental name, in accordance to where the substituent groups are attached. 4-ethyl-2,3-dimethylheptane

Practice Name the following compound:

Practice Draw the structural formula of 2-ethyl-3-methylpentane.

Practice Draw the structural formula of 4-methyl-2-pentene

Isomers Isomers are compounds that have the same molecular formula, but different molecular structures. Although they may have identical chemical formulas, the arrangement of their atoms are different, giving them different chemical properties.

Isomers: Example

Practice (June 2017) Which compound is an isomer of C2H5OC2H5? (1) CH3COOH (2) C2H5COOCH3 (3) C3H7COCH3 (4) C4H9OH

Practice Draw two isomers of pentene.