Intro to organic chemistry (orgo) SCH4U – Unit B

Organic Compounds Organic chemistry: chemistry of carbon compounds Exceptions are oxides of carbon (CO2 and CO), carbonates, bicarbonates, and cyanides Carbon atoms are generally bonded to: Each other Hydrogen atoms Other specific elements (O, N, S, P and others)

Why study organic chemistry? Life is carbon-based. Everyone is made up of organic compounds. There are more known carbon compounds than any other element. There are several million known organic compounds with ~30,000 more being “discovered” each year. Some common organic compounds include plastics, synthetic and natural fibres, dyes, drugs, pesticides, lighter fluid, and gasoline.

The carbon atom Carbon has four valence electrons allowing it to form four bonds with other atoms by sharing its electrons This results in a tetrahedral shape Carbon forms covalent bonds (sharing of electrons) with carbon atoms

Classification Since organic compounds are composed almost entirely of carbon, they are sometimes referred to as hydrocarbons Hydrocarbons can be divided into: Aliphatics: carbon atoms in an open chain structure; may have branches, but no rings Alicyclics: carbon atoms arranged in a ring structure Aromatics: structures related to benzene (C6H6)

Classification Aliphatics can be further categorized into: Alkanes: contains only single bonds (saturated) Alkenes: contains at least one double bond (unsaturated) Alkynes: contains at least on triple bond

Constitutional Isomers Stereoisomers Diastereomers Enantiomers

Constitutional Isomers Stereoisomers Isomers have same molecular formula Atoms bonded in a different sequence Atoms bonded in same sequence Also known as structural isomers Differ in 3D orientation of atoms in space

Isomers Diastereomers Enantiomers Based on a double bond Mirror images of each other around a single carbon atom Carbon atoms with different types of atoms At least one carbon atom bonded to four different types of atoms or groups cis isomer when two identical groups or atoms are on the same side trans isomer when two identical groups or atoms are on the opposite side

Diagrams & formulas A number of different (but related) diagrams used to express structures in organic chemistry: Empirical molecular formula Expanded molecular formula Complete structural formula Condensed structural formula Line structural formula 3D structural formula

Alkanes # of carbons Prefix 1 Meth- 6 Hex- 2 Eth- 7 Hept- 3 Prop- 8 Oct- 4 But- 9 Non- 5 Pent- 10 Dec-

Alkanes Only single bonds present in the main chain General formula is CnH2n+2 Form a tetrahedral shape Note: more on shapes in the next unit Create a 109.5° angle between bonds Considered “saturated” because no other hydrogen atoms can be added Always end in “~ane”

Nomenclature Three parts to organic chemistry nomenclature: Prefix: indicates number, type and location of branches and/or functional groups (if any) Root: indicates the number of carbon atoms in the main (parent) chain Suffix: indicates the number and location of double or triple bonds (if any) and/or highest priority functional group

Let’s draw alkanes! Draw all ten basic alkanes and name them.

Alkyl groups and branching Each branch of a hydrocarbon is referred to as an alkyl group (if it contains only C and H) Alkyl groups use the same basic roots as alkanes Alkyls always end in “~yl” Also contain a number and hyphen in front to indicate location on the main carbon chain Example: 2-methyl pentane

Alkyl groups and branching Find the longest carbon chain and assign sequential numbers to each carbon Assign these numbers temporarily starting from both ends of the carbon chain Ultimately will select only one set of numbers to use The goal is to use the numbering along the carbon chain that gives the lowest values assigned to branches

Alkyl groups and branching Let’s try some! Draw 3-ethyl octane…

Alkyl groups and branching

Alkyl groups and branching When there is more than one branch, they are listed in front of the root and suffix according to alphabetical order of the name of the alkyl group Try naming… 4-ethyl 3-methyl heptane

Alkyl groups and branching If there is more than one of any given alkyl group Indicate all the number for the positions using commas to separate the numbers, and Use prefixes (on the prefixes – confused yet?) to indicate the number present

Alkyl groups and branching Try naming… 5,6-diethyl-3,3,4-trimethyl nonane

Alkenes At least one double bond present in the main chain General formula is CnH2n Form a trigonal planar shape Note: more on shapes in the next unit Create a 120° angle between bonds Considered “unsaturated” because other hydrogen atoms can be added Always end in “~ene”

Nomenclature Identify and name the longest carbon chain that CONTAINS THE DOUBLE BOND(S). Number the carbons in the chain so that the two carbons involved in the double bond have the lowest possible numbers. If the double bond is equidistant from both ends, number the chain so that the substituent(s) have the lowest possibly number. Follow same rules for identifying and naming prefixes.

Nomenclature Try naming this… 2-ethyl 1-pentene

Nomenclature Now let’s draw 1-butene and 2-butene… 1-butene 2-butene

Nomenclature Let’s try a structure with more than one double bond… 1,3-pentadiene

Nomenclature Let’s put everything together and name… 4-ethyl-3,6-dimethyl 1,2,4-octatriene

Diastereomers Consider the following compounds… cis-2-butene trans-2-butene 2-methyl- 1-propene

Diastereomers Not superimposable upon one another Result from lack of free rotation around the double bond Priorities are assigned to the two groups attached to the carbon atoms on either side of the double bond (starting with the carbon to the left of the double bond) based on atomic number Largest atomic number at the first point of difference has the highest priority

Diastereomers If two highest priority groups are on the same side of the double bond (top or bottom)… cis configuration If two highest priority groups are on the opposite side of the double bond… trans configuration

Alkynes At least one triple bond present in the main chain General formula is CnH2n-2 Form a linear shape Note: more on shapes in the next unit Create a 180° angle between bonds Considered “unsaturated” because other hydrogen atoms can be added Always end in “~yne”

Nomenclature Identify and name the longest carbon chain that CONTAINS THE TRIPLE BOND(S). Number the carbons in the chain so that the two carbons involved in the triple bond have the lowest possible numbers. If the triple bond is equidistant from both ends, number the chain so that the substituent(s) have the lowest possibly number. Follow same rules for identifying and naming prefixes.

Nomenclature Try naming this… 3,4-dimethyl 1-hexyne

Nomenclature Now let’s draw 1-butyne and 2-butyne… 1-butyne 2-butene

Nomenclature Let’s try a structure with more than one triple bond… 2,4-hexadiyne

Nomenclature Let’s put everything together and name… 4-ethyl-4,5-dimethyl 2,6-octadiyne

Alicyclics Connected end-to-end forming a ring Have single and/or double bonds present in the main chain General formula is CnH2n Can be “saturated” or “unsaturated” Suffix changes depending on presence of double bonds Prefix used is always “cyclo~” before the root

Nomenclature Try naming… cyclobutane cyclo-1-pentene cyclopent-1-ene

Nomenclature Try drawing… cyclo-1,4-hexadiene 2,7-diethyl-4-methyl cyclo-1,3,5-heptatriene

Aromatics Based on benzene and the presence of benzene- like rings Benzene is a six-carbon ring with three double bonds Cyclo-1,3,5-hexatriene However, the electrons in the double bonds are actually spread over the whole molecule = delocalized Benzene actually has six identical “1 ½” bonds

Aromatics Creates greater stability in the molecule These “1 ½” bonds do not behave/react like double bonds Molecules that have this type of sharing are referred to as aromatic compounds Benzene

Aromatics Some common aromatics… benzene napthalene antracene

Nomenclature Number carbons in benzene ring assigning lowest number to a branch. If more than one branch exists, start numbering at the branch that contains the group with the highest priority (most complex). Name branches attached to the benzene ring, assigning numbers to each branch. If only one branch is present, a number does not need to be assigned. Branches are placed before the root as a prefix.

Nomenclature Priority of branches on benzene… Highest priority -OH -NH2 -F, -Cl, -Br, -I -CH2CH2CH3 -CH2CH3 Lowest priority -CH3

Nomenclature When benzene has only two branches, position numbers do not have to be used Instead, prefixes ortho-, meta-, and para- replace position numbers 1,2-dimethyl benzene ortho-dimethyl benzene

Nomenclature 1,3-dimethyl benzene 1,4-dimethyl benzene meta-dimethyl benzene para-dimethyl benzene

Nomenclature IUPAC has retained many of the common names for aromatics…

Nomenclature Let’s try naming… 3-ethyl-5-methyl phenol

Nomenclature Let’s try drawing… 2,6-diethyl-3-methyl benzaldehyde

Nomenclature For use when: Naming compounds with >1 fxn’l group Naming compounds with a complicated substituent

Nomenclature Try naming… 3-phenyl hexane

Nomenclature Try drawing… 4,6-diphenyl 2-octene

Up next That covers the basics of hydrocarbons in organic chemistry. Next we will cover functional groups!