Chapt 21 Hydrocarbons [Selected] 21.1 Introduction to Hydrocarbons 21.2 Alkanes [Straight-Chain Only] 21.3 Alkenes & Alkynes (added) 21.4 Hydrocarbon Isomers [also with O] Mhr 082614, edited, 44 slides not hidden. Added FHS slides to include information on alkenes and alkynes.

Section 21.1 Introduction to Hydrocarbons Hydrocarbons are carbon-containing organic compounds that provide a source of energy and raw materials. Explain the terms organic compound and organic chemistry. Identify hydrocarbons Recognize the different ways that hydrocarbon molecules may be represented (molecular formula, structural formula, ball-and-stick model, etc.) and convert a molecular formula into a valid structural formula and vice versa, Distinguish between saturated and unsaturated hydrocarbons.

Section 21.1 Introduction to Hydrocarbons Key Concepts Organic compounds contain the element ?? Hydrocarbons are organic substances composed of carbon and ??. The major sources of hydrocarbons are petroleum and natural gas.

Essential Organic Chemistry Bond – force that hold atoms together in compounds Carbon atom (C) always forms 4 bonds with other atoms; bond represented by a line Hydrogen can only form one bond

Simplest Hydrocarbon - Methane Chemical (molecular) formula: CH4 Structural formula: C H Chemical bond Carbon atom with 4 bonds

Chapt 21 Hydrocarbons [Selected] 21.1 Introduction to Hydrocarbons 21.2 Alkanes 21.4 Hydrocarbon Isomers [also with O]

Section 21.2 Alkanes Alkanes are hydrocarbons that contain only single bonds. Name a straight-chain alkane from its molecular formula or by examining its structure (up to octane). Draw the structural formula or write the molecular formula of a straight-chain alkane when given its name (up to octane).

Alkanes Simple Alkanes – hydrocarbons with only single bonds and no ring structures All have formula CnH2n+2 n = integer All have names ending in “ane” Simplest = methane Chemical (molecular) formula: CH4 Structural formula: C H Chemical bond Carbon atom with 4 bonds

Alkanes n = 2 ethane Chemical (molecular) formula: C2H6 Structural formula: n = 3 propane Chemical (molecular) formula: C3H8 C H C H

Ethane Most alkanes rotate freely about the single bond between carbon atoms

Two Equivalent Butane Molecules Right hand structure is twisted version of left hand structure 22

Simple Hydrocarbons - Alkanes Condensed formula helps to see structure Butane C4 shown as straight-chain isomer Type of Formula Molecular Structural Ball-and-Stick Space Fill Condensed CH3CH3 CH3CH2CH3 CH3CH2CH2CH3

Hydrocarbons – Straight-Chain Alkanes Type of Formula Name Molecular Condensed

Chapt 21 Hydrocarbons [Selected] 21.1 Introduction to Hydrocarbons 21.2 Alkanes [Straight-Chain Only] 21.3 Alkenes & Alkynes 21.4 Hydrocarbon Isomers [also with O]

Section 21.3 Alkenes & Alkynes Alkenes are hydrocarbons that contain at least one double-bond; Alkynes are hydrocarbons that contain at least one triple-bond. Name a straight-chain alkene or alkyne from its molecular formula or by examining its structure (up to oct-). Draw the structural formula or write the molecular formula of a straight-chain alkene or alkyne when given its name (up to oct-).

Alkenes Alkenes- hydrocarbons that have one or more double bonds between Carbons Unsaturated hydrocarbons Naming: prefix + ene

Naming and Drawing Alkenes Prefix Name Structure Eth- Ethene H-CH=CH-H Prop- Propene H-CH=CH-CH2-H But- 1-Butene H-CH=CH-CH2-CH2-H Pent- 1-Pentene H-CH=CH-CH2-CH2-CH2-H Hex- 1-Hexene H-CH=CH-CH2-CH2-CH2-CH2-H Hept- 1-Heptene H-CH=CH-CH2-CH2-CH2-CH2-CH2-H Oct- 1-Octene H-CH=CH-CH2-CH2-CH2-CH2-CH2-CH2-H

Doubles Bonds Can Move, Changes Name of Molecule Prefix Name Structure But- 1-Butene H-CH=CH-CH2-CH2-H 2-Butene H-CH2-CH=CH2-CH2-H Pent- 1-Pentene H-CH=CH-CH2-CH2-CH2-H 2-Pentene H-CH2-CH=CH-CH2-CH2-H Hex- 1-Hexene H-CH=CH-CH2-CH2-CH2-CH2-H 2-Hexene H-CH2-CH=CH2-CH2-CH2-CH2-H 3-Hexene H-CH2-CH2-CH=CH-CH2-CH2-H

Alkynes Alkynes- are hydrocarbons that have one or more triple bonds between Carbons Unsaturated hydrocarbons Naming: prefix + yne Example: Ethyne (Acetylene) used as a fuel in welding.

Naming and Drawing Alkynes Prefix Name Structure Eth- Ethyne H-C=C-H Prop- Propyne H-C=C-CH2-H But- 1-Butyne H-C=C-CH2-CH2-H Pent- 1-Pentyne H-C=C-CH2-CH2-CH2-H Hex- 1-Hexyne H-C=C-CH2-CH2-CH2-CH2-H Hept- 1-Heptyne H-C=C-CH2-CH2-CH2-CH2-CH2-H Oct- 1-Octyne H-C=C-CH2-CH2-CH2-CH2-CH2-CH2-H Cn H(2n-2)

Chapt 21 Hydrocarbons [Selected] 21.1 Introduction to Hydrocarbons 21.2 Alkanes [Straight-Chain Only] 21.3 Alkenes & Alkynes 21.4 Hydrocarbon Isomers [also with O]

Section 21.4 Hydrocarbon Isomers Some hydrocarbons [and other compounds] have the same molecular formula but have different molecular structures. Define the terms isomer, structural isomer, and stereoisomer. Categorize molecular structures as being structural isomers, stereoisomers or as not being isomers. Distinguish between geometric (diastereomers) and optical isomers (enantiomers) Differentiate between geometric isomers with cis- and trans prefixes. Describe describe the structural characteristics that are associated with optical isomers

Section 21.4 Hydrocarbon Isomers Some hydrocarbons [and other compounds] have the same molecular formula but have different molecular structures. Generate isomers of compounds containing oxygen in addition to carbon and hydrogen

Structural (Constitutional) Types of Isomers All Isomers Structural (Constitutional) Stereoisomers (Configurational) Diastereomers Enantiomers (optical) Geometric (Cis-trans) Other diastereomers (>1 chiral centers)

Making Butane (C4H10) From Propane or propane (C3H8)

Butane C4H10. = Not isomers – carbons connected in same way and forms can convert from one to the other by rotating around a bond = Structural isomers – carbons connected in different way; bond must be broken to convert one form into the other

Structural Isomers of C4H10 Butane, BP = 0°C Isobutane, BP = -12°C 47

Structural Isomers of C5H12 (Pentane) n-pentane isopentane neopentane Longest continuous carbon chain: pentane 5 isopentane 4 neopentane 3

# of Alkane (CnH2n+2) Structural Isomers Molecular Formula Possible # Isomers C4H10 2 C11H24 159 C5H12 3 C12H32 355 C6H14 5 C15H32 4,347 C7H16 9 C20H42 366,319 C8H18 18 C30H62 4,111,846,763 C9H20 35 C40H82 62,481,801,147,341 C10H22 75

Structural (Constitutional) Types of Isomers All Isomers Structural (Constitutional) Stereoisomers (Configurational) Diastereomers Enantiomers (optical) Geometric (Cis-trans) Other diastereomers (>1 chiral centers)

Enantiomers - Optical Isomers Tied to concept of non superimposable mirror images Familiar example – hands: left & right hands are mirror images but do not superimpose

Non-Superimposable Mirror Images Only when C attached to 4 different groups When this occurs, C variously referred to as a chiral center, asymmetric carbon, stereogenic center, or stereocenter 67

Identifying Chiral Centers Examine each tetrahedral carbon atom and look at four groups (not the four atoms) bonded to it If groups all different, have a chiral (stereogenic) center

Chiral Molecules - Entantiomers A pair of nonsuperimposable mirror images are called a pair of enantiomers – these molecules will be optical isomers of each other 69

Non-Superimposable Mirror Images Chiral molecule – mirror images are enantiomers (optical isomers) 72

Structural Isomers of C7H16 (Heptane) * * Isomers marked with * have asymmetric carbons (have enantiomers – optical isomers)

Optical Isomers of 3-methylhexane Tro, Chemistry: A Molecular Approach 77 77

Impact of Chirality Many natural molecules are chiral and most natural reactions are affected by optical isomerism; e.g. D- & L-amino acids! Many drugs are optically active, with only one enantiomer being beneficial (or harmful, e.g. thalidomide

Structural (Constitutional) Types of Isomers All Isomers Structural (Constitutional) Stereoisomers (Configurational) Diastereomers Enantiomers (optical) Geometric (Cis-trans) Other diastereomers (>1 chiral centers)

Structural (Constitutional) Types of Isomers All Isomers Structural (Constitutional) Stereoisomers (Configurational) Diastereomers Enantiomers (optical) Geometric (Cis-trans) Other diastereomers (>1 chiral centers)

Stereoisomers – No Chiral Centers Groups on same or opposite sides of double bond – diastereomers (spatially different but not mirror images)

Isomers with CHO Compounds With carbon, hydrogen and oxygen (CHO) present, isomers become more varied Rule: O in these compounds forms 2 bonds O found in form of alcohol (COH), ether (COC), or carbonyl (C=O) group

Isomers of C3H8O 2 structural isomers in form of alcohol 1 structural isomer in form of ether ethyl methyl ether propan-1-ol propan-2-ol

Summary – Isomers Structural Isomers