Chem Chapter 9 - Hydrocarbons: an introduction to organic molecules

two properties that make carbon unique

1. carbon atoms can form strong, stable chains, lined by covalent bonds

2. carbon atoms can form four covalent bonds, allows each carbon atom in a chain to form bonds to additional atoms

bonding patterns for carbon atoms

has 4 valence electrons and four empty spaces in its valence shell

1. four single bonds

2. one double bond + two single bonds

3. two double bonds

4. one triple bond + one single bond

valence shell electron pair repulsion model

the principle that valence electrons around an atom arrange themselves to be as far apart as possible (VSEPR)

tetrahedral arrangement

an arrangement in which four bonded atoms are equally spaced around a central atom

• the four atoms around a carbon atom always form a tetrahedral arrangement

solid wedge

represents a bond that is coming toward you (out of paper)

dashed wedge

represents a bond that is going away from you (into paper)

hydrocarbons

compounds that contain only carbon and hydrogen atoms (simplest of all organic compounds bc only contains 2 elements)

alkane

an organic compound / hydrocarbon that contains only single bonded carbon and hydrogen atoms

alkene

contain at least one carbon to carbon double bond

alkyne

contains at least one carbon to carbon triple bond

aromatic compound (arene)

contains a six membered ring of carbon atoms linked by alternating single and double bonds (has 3 extra electrons that float freely within the ring of carbon atoms)

linear alkanes

an alkane in which the carbon atoms form a single continuous chain with single bonds

• smallest linear alkane is methane

full structured formula

a way to represent an organic molecule in which all atoms and chemical bonds are drawn out

• does not shown non bonding electrons

condensed structural formula

an abbreviated way to write structural formula, represents an organic molecule that lists the # of hydrogen atoms beside the atom to which they are bonded

ex. CH3-CH2-CH2-CH3

common ways to represent an organic molecule

1. wedged dash structure

2. full structural formula

3. condensed structural formula

4. line structure

5. molecular formula

line structure

structure of organic compound using zigzag lines to represent hydrocarbon chains, no C labels / omit H all together

molecular formula

useful for writing balanced equations (C₆H₁₄)

branched alkane

an alkane in which the carbon atoms do not form a single continuous chain (ex. isobutane)

isomers

compounds that have the same molecular formula but different structures

• different arrangement of atoms will often produce a molecule with dramatically different physiological properties

constitutional isomers

molecules that have the same molecular formula but differ in the order in which the atoms are connected to one another

• have different shapes = different physical and chemical properties

cycloalkane

an alkane in which the carbon atoms form a ring

methane

CH₄

ethane

C₂H₆

propane

C₃H₈

butane

C₄H₁₀

pentane

C₅H₁₂

hexane

C₆H₁₄

heptane

C₇H₁₆

octane

C₈H₁₈

nonane

C₉H₂₀

decane

C₁₀H₂₂

cycloalkanes and alkanes

are not isomers, cycloalkanes don’t have hydrogen ends, so cycloalkanes always have 2 fewer hydrogens

saturated hydrocarbons

a hydrocarbon that does not contain any double or triple bonds, contains more hydrogen atoms then hydrocarbons with double, triple bonds

To name a branched alkane

1. start with identifying the longest continuous carbon chain in the molecule (principal carbon chain)

2. identify the branches that are attached to the principal chain (alkyl groups)

3. name alkyl groups by replacing “ane” ending of the corresponding alkane with “yl”

4. for chains that contain 3 or more carbon atoms, there is more than one possible alkyl group depending on where we remove the hydrogen atom

5. propyl, butyl, and so forth are reserved for the alkyl groups that are missing a hydrogen from the end of the chain

principal carbon chain

longest continuous carbon chain

alkyl groups

fragment of an organic compound consisting of an alkane that is lacking / one hydrogen atom has been removed, which allows alkane to be attached to a larger molecule

methyl

number of carbon atoms = 1

condensed structure = CH3

ethyl

number of carbon atoms = 2

condensed structure = CH2-CH3 

propyl

number of carbon atoms = 3

condensed structure = CH2-CH3-CH3

isopropyl

number of carbon atoms = 3

condensed structure = CH3-CH-CH3 (missing the hydrogen in the middle instead of the end

butyl

number of carbon atoms = 4

condensed structure = CH2-CH2-CH2-CH3

naming an alkane with only one branch

focus on carbon chain and ignore hydrogen atoms

1. identify and name the principal carbon chain and the alkyl group

2. # the carbon atoms in the principal chain, starting from the end that is closest to the alkyl group

3. write the name of the branch in front of the name of the principal chain

naming a cycloalkane that is attached to an alkyl group

rules are similar, we do not write # to show location of alkyl group

name one branch step 1

identify and name the principal carbon chain and the alkyl group

name one branch step 2

# the carbon atoms in the principal chain, starting from the end that is closest to the alkyl group

• use #’s to tell where the alkyl group is attached to the principal chain

name one branch step 3

write the name of the branch in front of the name of the principal chain

• rules are designed to give every organic molecule a unique name that does not depend on how we draw the structure of the molecule

same IUPAC name 

if 2 structural formulas have the same IUPAC name, they represent the same chemical compound

different IUPAC name

if 2 structural formulas have different IUPAC names but the same chemical formula, they must be isomers 

naming an alkane with more than 1 branch

1. the alkane has 2 or more identical branches - use prefixes di, tri, tetra, etc to show # of identical alkyl groups

2. the molecules contain 2 or more different branches - molecules that have alkyl groups that are different sizes, list the alkyl groups alphabetically

3. the molecule contains both identical and different branches - if we have 2 or more identical branches ignore the prefixes when alphabetizing names

4. both ends of the principal chain are the same distance from a branch - if this happens we simply proceed to next branch thats closest

naming more than one branch (2 or more identical branches)

the alkane has 2 or more identical branches - use prefixes di, tri, tetra, etc to show # of identical alkyl groups

• each alkyl group gets a #, separate the # using commas

naming more than one branch (contain 2 or more different branches)

the molecules contain 2 or more different branches - molecules that have alkyl groups that are different sizes, list the alkyl groups alphabetically

naming more than one branch (contain both identical and different branches)

the molecule contains both identical and different branches - if we have 2 or more identical branches ignore the prefixes when alphabetizing names

naming more than one branch (both ends are same distance)

both ends of the principal chain are the same distance from a branch - if this happens we simply proceed to next branch thats closest

organic compounds are classified by

functional groups

functional groups

any bond or group of atoms that is not present in alkane and that gives a compound the ability to undergo specific chemical reactions

unsaturated hydrocarbon

any hydrocarbon that contains at least one double or triple bond

alkenes

molecules that contain a carbon-carbon double bond, double bond is referred to as the “alkene functional group”

• contain a trigonal planar arrangement of atoms

alkynes

molecules that contain a carbon-carbon triple bond, bond known as alkyne functional group

• triple bond and neighboring bonds line up

trigonal planar arrangement

an arrangement in which 3 bonded atoms are equally spaced around a central atom

alkenes and alkynes can be named using IUPAC rules

name must describe hydrocarbon framework of molecule, identify the functional group, and tell where the functional group is located 

alkenes and alkynes naming rules

1. name the compound as if it were an alkane, ignoring the functional group

2. change the “ane” ending of the alkane name to “ene” for an alkene or “yl” for alkyne

3. # of carbon-carbon bonds starting from the end closest to the functional group and use these #’s to identify the position of the multiple bond

4. assemble the name by writing the # from step 3 followed by the name, use hyphen to seperate #’s from words

cycloalkenes

when a hydrocarbon contains an alkene group within a ring of carbon atoms

• contain double bond within a ring of carbon atoms

name cycloalkenes

change ending of corresponding cycloalkane from “-ane” to “-ene”

in branched alkene or alkyne

the functional group determines the principal chain

naming branched alkene or alkyne

2 additional rules

1. the principal chain is the longest chain that includes the functional group

2. the principal chain is numbered from the side closest to the functional group, regardless of the positions of the branches

3. list the alkyl groups

trivial names

a traditional name for a chemical substance that is not part of the IUPAC system

flexible molecules

alkanes are flexible, able to adapt to a range of shapes while retaining the tetrahedral arrangement around each carbon atom

non flexible molecules

carbon-carbon double bonds do not permit free rotation

cis and trans isomeric forms

linear alkenes have cis and trans isomeric forms, if number is 2 or larger the alkene can either be cis or trans

cis

has 2 of the same atom / group on the same side

trans

has 2 of the same atom / group on opposite sides (one up, one down)

stereoisomers

molecules that have the same chemical formula but differ in the relative positions of the groups surrounding a single atom

benzene

C₆H₆

• has 3 extra electron pairs that flow freely around ring 

aromatic compounds

compounds that contain the benzene ring, alkyl groups can be added to benzene rings

large molecules have

higher melting and boiling points