chapter 6 slides 2017 - calvin university

9/29/17

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General, Organic, and Biochemistry Chapter 6: Chapter Opener

CHAPTER 6: HYDROCARBONS & STRUCTURE • Our relatively diverse diet

is remarkably simple at the chemical level:ü Carbohydratesü Lipidsü Proteinsü Nucleic acidsü Vitamins/micronutrients

• The chemical composition of all these biomolecules is organic chemistry

Chapter 1: Measurement, Atoms, and Molecules

MANY ELEMENTS….ONLY A FEW BUILDING BLOCKS TO BIOMOLECULES

Hydrocarbons

• Hydrocarbons can be arranged in a remarkable variety of ways due to the flexible bonding available to carbon atoms

• The simplest classification system is based on the type of bond formed between carbon atoms

General, Organic, and Biochemistry Chapter 6

SIMPLE ORGANIC STRUCTURAL CLASSES

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• Nonpolar:Ø Composed of all nonpolar bonds

• Poor water solubility:Ø Hydrophobic = “water fearing”

Ø Hydrophilic = “water loving”


COMMON PROPERTIES OF HYDROCARBONS

Petroleum Products

Natural Gas

• Alkanes are the simplest class of hydrocarbonsØ Composed of carbons sharing only SINGLE bonds

Ø Can form (very!) long chains

• Each carbon will form 4 separate covalent bonds


ALKANES – SINGLE BONDED CARBONS

Ø The molecular geometry around each carbon is tetrahedral

• Alkane Nomenclature: 1. Number of carbons: specific root for each number2. Bond structure: always end with –ane


ALKANES NOMENCLATURE

NumberofCarbons

RootPrefix

AlkaneName

MolecularFormula

1 Meth Methane CH4

2 Eth Ethane C2H6

3 Prop Propane C3H8

4 But Butane C4H10

5 Pent Pentane C5H12

6 Hex Hexane C6H14

7 Hept Heptane C7H16

8 Oct Octane C8H18

9 Non Nonane C9H20

10 Dec Decane C10H22

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• Single bonds allow for rotation between adjacent carbon atoms

• Alkanes are highly flexible molecules!


ALKANES ARE FLEXIBLE MOLECULES

• Alkanes do NOT have to be linear….

• Branched alkanes are like trees

• Branching dramatically increases the varietyof organic molecules


BRANCHED CHAIN ALKANES

• Structural isomers are molecules with the same number & type of atoms, but different bond arrangements


STRUCTURAL ISOMERS

Consider a family of 5 carbon structural isomers

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• Organic chemists use condensed ways of drawing hydrocarbons to simplify structures

• There are three ways to represent hydrocarbons:


REPRESENTING ALKANE STRUCTURES

Complete Structural Formulas

Condensed Structural Formulas

Skeleton Line Structures

• Branched alkane nomenclature depends on: 1. Number of atoms in the longest C-C chain

2. The length of side-chains with an –yl on the end

3. The location of side-chains


NOMENCLATURE FOR BRANCHED ALKANES

4-methyl-heptane

• Alkenes contain C=C double bondsØ Hydrocarbons with double bonds have fewer hydrogen

atoms, and are therefore unsaturated

• Carbons with double bonds have only three electron groups to consider in their shape:Ø Alkene molecular geometry is trigonal planar


ALKENES – DOUBLE BONDED CARBONS

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• Alkene Nomenclature: 1. Number of carbons: specific root for each number2. Bond structure: always end with –ene


ALKENE NOMENCLATURE

NumberofCarbons

RootPrefix

AlkaneName

MolecularFormula

1 Meth - -

2 Eth Ethene C2H4

3 Prop Propene C3H6

4 But Butene C4H8

5 Pent Pentene C5H10

6 Hex Hexene C6H12

7 Hept Heptene C7H14

8 Oct Octene C8H16

9 Non Nonene C9H18

10 Dec Decene C10H20

• Double bonds prevent rotation between adjacent carbon atoms:Ø Such bonds are said to be constrained

• Consider two closely related molecules:


ALKENE ROTATION IS CONSTRAINED

An alkane:ButaneC4H10

An alkene:ButeneC4H8

• Geometric Isomers are molecules with opposite rotations around a C=C double bond

• Naming of each isomer depends on arrangement of priority groups around the C=C bond


ALKENES FORM GEOMETRIC ISOMERS

cis isomer(same side)

trans isomer(opposite sides)

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General, Organic, and Biochemistry Chapter 6: Figure 6.12

GEOMETRIC ISOMERS ARE BIOLOGICALLY IMPORTANT FOR VISION

General, Organic, and Biochemistry Chapter 6: Figure 6.12

GEOMETRIC ISOMERS ARE BIOLOGICALLY IMPORTANT FOR VISION

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• Alkynes contain C C triple bondsØ Composed of carbons with 6 shared electrons

• Carbons with triple bonds have only two electron groups to consider in their geometry:Ø Molecular geometry is linear


ALKYNES – TRIPLE BONDED CARBONS

C2H2

acetylene

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• Double and triple bonds take priority in naming branched hydrocarbons:Ø Number of atoms in the longest C-C chain that

also contains the double or triple bond


NOMENCLATURE FOR BRANCHED ALKANES

2-ethyl-1-buteneHow do we name this molecule?

• Hydrocarbons do NOT have to be linear


MAKING RINGS WITH CARBON• Hydrocarbons do NOT have to be linear….or

branched….

• Cyclic hydrocarbons (“rings”) are another type of structural isomer commonly found in hydrocarbons

Ø Cyclic hydrocarbons are unsaturated

Ø Note how the backbone of cyclic alkanes is “kinked” (not flat)


BOND STRAIN IN CYCLIC HYDROCARBONS• The # of carbons in a ring affects bond angles

Ø Typical cyclic hydrocarbons have 5-8 carbons

• Fewer or more carbons are possible, but create “ring strain”

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cyclopropane

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• Hydrocarbon rings simply use the prefix cyclo- in front of the alkane name to denote the structure:Ø All C-C single bonds: cyclo____aneØ Containing a C=C double bond: cyclo_____ene


NOMENCLATURE FOR CYCLIC HYDROCARBONS

Pentane (C5H12) Cyclopentane (C5H10)

Note how the C:H ratio helps to identify a cyclic hydrocarbon from a linear or branched hydrocarbon

H = 2CH = 2C + 2


CARBON RINGS WITH DOUBLE BONDS• Cyclic hydrocarbons with C=C double bonds in

addition to C-C single bonds are more unsaturated:Ø Cyclopentane

Ø Cyclopentene

• Aromatic rings are formed when all carbons in a ring share C=C double bonds:Ø All carbons in the ring have trigonal planar geometry

This makes aromatic rings very flat

C5H10 C5H8


COMPLEX CYCLIC HYDROCARBONS• Carbon rings can have their remaining hydrogen

atoms substituted with other chemical groupsØ These are called functional groups (Chapter 7)Ø Impart new shapes & chemical properties to organic

ringsBenzene6-carbon aromatic ring

Functional groups can be added at any carbon

Remember your nomenclature rules!

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EMBRACING THE COMPLEXITY• Biologically relevant molecules (biomolecules)

are complex organic chemical unitsØ Carbon “backbone” decorated with a variety of

functional groupsØ Functional groups (-OH, -NH2, etc) can add new

properties (e.g. polarity) to the hydrocarbon backbone

What sort of hydrocarbon shapes are present in this molecule?

What sort of functional groups are attached?

Cholesterol


SHAPE MATTERS!!• Simple changes to biological hydrocarbons can have

dramatic effects on physical properties

• Biochemistry is largely a study of how small chemical changes alter shape & function of biomolecules:

Saturated fatty acidUnsaturated fatty acid

Palmitic acid Linolenic acid

chapter 6 slides 2017 - calvin university

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