Organic Chemistry Chemistry of Carbon Compounds (except oxides, carbides, & carbonates)

Why so many C compounds? Carbon atoms can bond with other carbon atoms in chains, rings, and networks. covalentBonds are covalent.

Lewis Diagram of C C Carbon has 4 unpaired electrons. It can form 4 covalent bonds. Note: C can form only 3 bonds to any other single C atom.

Bonding Capacity of H, O, etc. H can form only 1 bond. O and S like to form 2 bonds. The halogens (F, Cl, Br, I) form only 1 bond. N and P form 3 bonds.

Properties of Covalent Substances molecular (also called molecular substances) Low melting & boiling points Poor conductors of heat & electricity May be soft or brittle Generally nonpolar – van der Waals forces Tend to dissolve in nonpolar solvents React more slowly than ionic compounds

Chemical Formulas show kind & number of atoms. CH 2 Cl 2 CH 4 CH 3 OH CH 3 Cl

Structural Formulas Show kind & number of atoms. Also show bonding patterns and approximate shapes of molecules. 2-D rep of 3-D object so structural formulas aren’t totally realistic. H H–C–H H

Structural Formulas – A single line represents one pair of electrons (a single bond). = A double line represents two pairs of electrons (a double bond).  A triple line represents three pairs of electrons (a triple bond).

Shape The 4 unpaired electrons around the C atom are located at the corners of a tetrahedron  apart.

Vocabulary Interlude Saturated SSaturated: organic compounds containing only Single bonds. UnsaturatedUnsaturated: organic compounds containing one or more double or triple bonds.

Vocabulary HydrocarbonsHydrocarbons: organic compounds containing only C and H. Homologous SeriesHomologous Series: a group of compounds with related structures and properties. Each member of the series differs from the one before it by the same additional unit.

Homologous Series The molecules have a fixed, numerical relationship among the numbers of atoms.

Condensed Structural Formula Shows kind & number of atoms Shows some structural information, but not all the details. Fits on 1 line of type. H H H CCC H–C–C–C–H H H H CCC Becomes CH 3 CH 2 CH 3

Alkanes Homologous series of saturated hydrocarbons. Release energy when burned. CH 4 H H–C–H H C 2 H 6 H H H–C–C–H H H C 2 H 6 is also written CH 3 CH 3

Above: 3 representations of CH 4. Below: Ball and stick model of ethane. Space-filling model

Alkanes or C n H 2n+2 C 3 H 8 H H H H–C–C–C–H H H H CH 3 CH 2 CH 3 Chemical Formula Structural Formula Condensed Structural Formula

Ball & stick model of propane. Bond angles = 109 .

4 th straight-chain alkane C 4 H 10 H H H–C–C–C–C–H H H Or CH 3 CH 2 CH 2 CH 3

Ball and Stick model of butane.

Alkanes: base unit CH 4 CH 3 CH 3 or C 2 H 6 CH 3 CH 2 CH 3 or C 3 H 8 CH 3 CH 2 CH 2 CH 3 or C 4 H 10 CH 3 CH 2 CH 2 CH 2 CH 3 or C 5 H 12 CH 2 Difference between each is CH 2

Naming straight-chain Alkanes Name describes molecule so you can draw it. aneaneAll alkanes have the suffix –ane. The prefix depends on the number of C’s.

Prefix# of C atoms Meth1 Eth2 Prop3 But4 Pent5 Hex6 Hept7 Oct8 Non9 Dec10

FormulaName CH 4 Meth + ane C2H6C2H6 C3H8C3H8 C 4 H 10 C 5 H 12 Ethane Propane Butane Pentane

Properties of Alkanes Change systematically with number of C’s As the number of C’s increases, the boiling point increases. –The molecules get heavier & harder to change into the gas phase.

Properties of Alkanes Low Reactivity Except readily undergo combustion – fuels Nonpolar – Don’t dissolve well in water. Low melting pts & boiling pts. (M.P. & B.P. increase with molecular mass) High vapor pressures

A.Low melting point B.High melting point C.Soluble in polar solvents D.Insoluble in nonpolar solvents Which property is generally characteristic of an organic compound? Correct response = A

A.CH 4 B.C 2 H 6 C.C 3 H 8 D.C 4 H 10 Which of the following compounds has the highest boiling point? Correct answer = D. In nonpolar covalent compounds, the boiling point depends on the strength of the van der Waals interactions. The van der Waals forces increase as the size of the molecule increases. (Bigger molecule, bigger electron cloud.)

Branched-chain alkanes Beginning with butane, C 4 H 10, there is more than 1 way to arrange the atoms. H H–C–H H H–C–C–C–H H H H

Branched alkane. Can’t link all the C’s without lifting pencil off the paper. Methyl propane

Isomers Compounds with the same molecular formula but different structural arrangement. The more C atoms there are in the formula, the more isomers there will be.  More possible ways to arrange them.

Isomers Different structures, different properties.Different structures, different properties. Isomers have different chemical and physical properties.

A note about isomers --- If you are comparing 2 structural formulas & you can superimpose them, they are not isomers – they are the same molecule! If you can rotate or flip one of the structural formulas & then superimpose it on the other one, they are not isomers – they are the same molecule!

These diagrams represent the same molecule. Represents bond to H

These diagrams represent the same molecule. Represents bond to H

These diagrams represent the same molecule. Represents bond to H

Two different molecules! Represents bond to H

Naming Branched-Chain Alkanes The goal of the name is to describe the molecule so you can draw it.

Naming branched-chain alkanes longest continuous chainFind the longest continuous chain or backbone of C atoms. (Bends don’t count!) base nameThe base name is derived from the number of C’s in the longest chain. Branchesinprefix branchends in “yl.”Branches are named in the prefix. Branches are also named by the number of C atoms. The “branch” part of the name ends in “yl.” assign numbers to the C’s in the backboneThe location of the branch is shown by assigning numbers to the C’s in the backbone. Number from the end that gives the lowest number for the branch. There may be more than 1 of the same type of branch. Use di, tri, etc.

H H–C–H H H–C–C–C–H H H H methyl Branch has 1 carbon – methyl. Branch has to be at C-2. (Only give the number if necessary.) Methyl propane C 4 H 10 CH 3 CH(CH 3 )CH 3 propane Longest continuous chain has 3 carbon atoms – propane.

H H–C–H H H H H–C–C–C–C–H H H H H–C–H H Longest continuous chain has 6 hexane carbon atoms. It’s a hexane. methyl Branch is 1 carbon long – methyl. 2 Branch is located at C-2. 2-methyl hexane C 7 H 16 CH 3 CH(CH 3 )CH 2 CH 2 CH 2 CH 3

A note about branches If you have several branches with the same # of C atoms, you can condense the name a little. 2-methyl 3-methyl pentane becomes 2,3- dimethyl pentane. The # of numbers must match the # of branches.

H H – C – H H H H H – C – C – C – C – H H H H–C–H H–C–H H H Longest continuous chain has 6 carbon atoms: hexane Branch is 1 carbon long: methyl Branch is located at C-3 3-methyl hexane C 7 H 16 CH 3 CH 2 CH 2 CH(CH 3 )CH 2 CH 3 CH 3 (CH 2 ) 2 CH(CH 3 )CH 2 CH 3

Alkenes hydrocarbonsAnother homologous series of hydrocarbons. one unsaturatedEach member contains one double covalent bond between C atoms.  So alkenes are unsaturated. General formula = C n H 2n

Naming Alkenes Names: # of C’s in parent chain gives prefix. Suffix = -ene. 1 st member is C 2 H 4, ethene. H H C=C H H H H

Alkenes with 4 or more C’s Number C atoms. Use lowest possible # to specify location of 1 st C in double bond.

Naming Alkenes Number C atoms in backbone. Give double bond the lowest possible number. H H H C=C–C–C–H H H C 4 H 8 CH 2 CHCH 2 CH 3 H H H H H–C–C=C–C–H H H C 4 H 8 CH 3 CHCHCH 3 1-butene2-butene

Naming Branched-Chain Alkenes Parent chain = longest chain that contains the double bond. Also, position of double bond, not branches, determines numbering of backbone. Give 1 st C in bond lowest possible #.

Properties of Alkenes Nonpolar – low solubility in H 2 O Fairly low M.P. & B.P. More reactive than alkanes – double bond = site of reactivity.

Alkynes Homologous series of unsaturated hydrocarbons that contain one triple bond. Each member contains one triple carbon- carbon bond. –Alkynes are unsaturated. General formula = C n H 2n-2

Naming Alkynes Name: Prefix depends on # of C’s. Suffix = -yne. If necessary, number the 1 st carbon atom at which the triple bond occurs.

H–C  C–HC 2 H 2 ethyne CHCH H H–C  C–C–H H H H H–C  C–C–C–H H H H H H–C–C  C–C–H H H C3H4C3H4 propyne CHCCH 3 C4H6C4H6 1-butyne CHCCH 2 CH 3 C4H6C4H6 2-butyne CH 3 CCCH 3

3 Homologous Series of HC’s Name of SeriesGeneral FormulaEnding AlkanesC n H 2n+2 -ane AlkenesC n H 2n -ene AlkynesC n H 2n-2 -yne

A.C 2 H 2 B.C 2 H 4 C.C 6 H 6 D.C 6 H 14 Which compound belongs to the alkene series? Correct answer = B. Alkenes follow the format C n H 2n. A & C are C n H n. D is C n H 2n+2.

A.C 2 H 2, C 2 H 4, C 2 H 6 B.C 2 H 4, C 3 H 4, C 4 H 8 C.C 2 H 4, C 2 H 6, C 3 H 6 D.C 2 H 4, C 3 H 6, C 4 H 8 In which group could the hydrocarbons all belong to the same homologous series? Correct answer = D. Members of a homologous series all have the same relationship between the atoms. Every compound in set D fits the formula C n H 2n.

A.Ethene B.Ethyne C.Propene D.Propane Which of the following is a saturated hydrocarbon? Correct answer = D. The alkanes are saturated.