Organic Notes Part I.notebook

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Notes on Organic Chemistry

Part I

Aliphatic Cyclic & Aromatic Hydrocarbons

Organic Notes Part I.notebook

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Organic chemistry is the study of carbon compounds. Most chemists in the world are employed as organic chemists. There are over 2 million organic compounds in existence with thousands of new ones being synthesized every year. Inorganic compounds, in contrast, number around 50 thousand. Why so many organic compounds? This comes from the carbon atom’s ability to bond with itself to form long chain and branched chain structures as well as cyclic structures. Organic compounds are molecular (covalent bonding between atoms) and exhibit the following properties:

1. They are generally nonpolar and thus insoluble in water.2. They are nonelectrolytes (except for weak organic acids)3. They have weak intermolecular forces of attraction – van der Waals forces and thus low melting points.4. The mechanisms of organic reactions generally involve high activation energies and thus organic compounds show reactivity

(compared to inorganic compounds).

Recall from you study of bonding that the carbon atom undergoes sp3 hybridization when bonding (forming four equivalent hybrid orbitals) and forms a tetrahedral structure when bonding with four other elements. Carbon atoms can also share two pairs of electrons (double bond) and three pairs of electrons (triple bond). When drawing the structural formulas or organic compounds keep in mind the number of shared pairs (dashes) atoms can have:

Carbon : 4 Nitrogen: 3Hydrogen: 1 Halogens: 1Oxygen: 2

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The organic compounds that we will be studying can be divided into two broad categories: aliphatic and aromatic hydrocarbons (and their derivatives) and functional groups. We will name organic compounds using IUPAC (International Union of Pure and Applied Chemists) rules. In general, the first part of a name (prefix) tells us the number of carbon atoms while the second part of the name (suffix) tells us the classification. You will need to memorize the following prefixes:

Prefix # C atoms Prefix # C atoms

meth 1 hex 6eth 2 hept 7prop 3 oct 8but 4 non 9pent 5 dec 10

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Organic Compounds

Aliphatic Hydrocarbons Aromatic Hydrocarbons Functional Groups

Aliphatic and Aromatic Hydrocarbons Functional GroupsCyclic Hydrocarbons

Straight chain, branched cyclic hydrocarbons compounds with a groupor cyclic hydrocarbons and having a benzene structure of atoms giving the their compoundtheir derivatives and their derivatives specific properties

Organic Notes Part I.notebook

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Aliphatic Hydrocarbons

Alkane family

– general formula is CnH2n+2

– all C to C bonds are single bonds; this is known as a saturated compound– suffix is “ane”– as you increase in molecular mass within the family the van der Waals forces increase and the melting and boiling points increase

draw methane, CH4

draw pentane:

note: as molecular weight of alkanes increases, VDW forces increase and boiling point increases (gasàliquidàsolid)l

Fossil fuels are mostly aliphatic hydrocarbons derived from the decomposition of once­living organisms. The energy provided by these compounds originally came from the sun. Petroleum is a mixture of fossil fuel hydrocarbons containing from 5 to 25 carbon atoms. Natural gas, which is usually associated with petroleum deposits, consists mostly of methane but also contains significant amounts of ethane, propane and butane.

The components of petroleum are separated on the basis of difference in boiling points by a process called fractional distillation. The 5 carbon to 12 carbon components make up the gasolines. Additional gasoline can be produced by breaking apart longer chain carbon molecules to smaller molecules in a process called pyrolytic cracking.

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May 16, 2016

Alkene Family

– general formula is CnH2n

– contain one C to C double bond; therefore unsaturated– suffix is “ene”

Draw ethane, C2H4

draw 2­hexene

Alkyne Family

– general formula is CnH2n­2

– contain one C to C triple bond; therefore unsaturated– suffix is “yne”

1st member: ethyne, C2H2 (also known as acetylene)

2nd member: propyne, C3H4

Dienes

– contain two C to C double bonds– suffix is “diene”

example: 1,4 pentadiene

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Aromatic Hydrocarbons

Benzene Family

– general formula is CnH2n­6

1st member is benzene, C6H6

The above structural formulas indicate alternate single and double bonds between the carbon atoms. An infrared spectrum of the benzene molecule reveals that in fact all the carbon to carbon bonds are identical in length and between a single and double bond in length. How do chemists explain this? They come up with a model in which an electron pair “flips” or resonates around the ring (as shown above). These are called resonance structures. The simplified way of drawing the structural formula for benzene is:

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2nd member is methylbenzene, C7H8

common name is toluene

CH3

Note that the methyl group is automatically on the 1 carbon .

3rd member is dimethylbenzene, C8H10 (common name is xylene)

CH3

Note: Isomers are compounds having the same chemical formula but different structural formulas. The greater the number of carbon atoms in a molecule, the greater the number of possible isomers.

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Substitution/Addition Groups:

halogens: alkyl groups: others:

­F fluoro ­CH3 methyl ­NO2 nitro­Cl chloro ­C2H5 ethyl­Br bromo ­C3H7 propyl­I iodo

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Practice Problems – Writing Structural formulas for Hydrocarbons and Their Derivatives

1. ethane: 7. 2­nitromethylbenzene:

2. 1,1­dibromopropane: 8. 1­chloro­4­ethylhexane:

3. 1,4­hexadiene: 9. 3­methylpentance:

4. chloroethane: 10. 1,2­dinitrobenzene:

5. 1,2­dichloropropane: 11. 3,4­dichloro­4­methyl­2­hexene:

6. nitrobenzene: 12. trichloromethane:

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