Organic Chemistry - Introduction

Transcription

1 It s All About Carbon! Unit 15: Organic Chemistry Lesson 15.1: Hydrocarbons Organic Chemistry - Introduction Organic chemistry is the study of compounds containing carbon. Animals, plants, and other forms of life consist of organic compounds. Nucleic acids, proteins, fats, carbohydrates, enzymes, vitamins, and hormones are all organic compounds. Biochemistry was developed later as the study of the chemical compounds and reactions in living cells. 1 Intro Organic Chemistry - Introduction Scientists had originally thought that organic compounds contained a vital force due to their natural origin. This was disproved by Friedrich Wöhler in Wöhler was able to make urea, a carbon compound found in human urine, in the laboratory from a mineral. Organic chemistry is an enormous field. In this unit we will investigate few (very few) of the fundamental concepts. Bonding in Organic Compounds Besides carbon, the most common elements in organic compounds are hydrogen, oxygen, nitrogen, sulfur, and the halogens. All of the preceding elements are non-metals, therefore organic compounds have covalent bonding. Intro Section 14.1 Properties of Carbon: Forms 4 bonds. Carbon s four single bonds form a tetrahedron with angles of o Why Carbon? Numbers and Types of Bonds for Common Elements in Organic Compounds Application of the octet rule indicates that these elements should bond as shown below: H O N C if you like Organic Chem = # bonds for each element 5 Section

2 Properties of Organic Compounds 1. Organic compounds are numerous. More than 2 million organic compounds are known (and 100,000 more are discovered or created each year) versus only 60,000 inorganic compounds. 2. Most carbon compounds are non-polar/ weakly polar a. Low melting/boiling point b. High vapor pressure 7 Properties of Organic Compounds 3. Most are immiscible in water 4. Most organic compounds are nonelectrolytes Organic acids are excerptions They are weak electrolytes 5. The undergo combustion: Powers the world 2C 8 H O 2 16CO H 2 O 6. They decompose when heated without oxygen back into carbon. This is how fossil fuels are made. 7. The have very complex, slow reactions. Catalysts are often used to increase reaction rates. 8 Hydrocarbons Hydrocarbons are the most simple organic compounds. Hydrocarbons contain only carbon (C) and hydrogen. (H) For classification purposes, all other organic compounds are considered derivatives of hydrocarbons. Hydrocarbons can be divided into aromatic and aliphatic hydrocarbons. Classification of Hydrocarbons Many can be isolated from crude oil mixtures. A lot of global unpleasantness is due to the need for hydrocarbons. Section 14.2 Section 14.2 Types of Hydrocarbons Aromatic: Have a ring structure. Example: Benzene (C 6 H 6 ) General Formula (C n H 2n-6 ) Aliphatic: Have a straight-chain structure. Example: Butane (C 4 H 10 ) Types of Aliphatic Hydrocarbons Saturated: Have only single bonds between C s The alkanes. General Formula C n H 2n+2. Suffix -ane Unsaturated: Have at least 1 double or triple bond between C s The alkenes: Have double bonds. General Formula C n H 2n Suffix -ene The alkynes: Have triple bonds. General Formula C n H 2n Suffix -yne 11 Propane Propene Propyne 12 2

3 A Chart For You Types of Hydrocarbons The three families of aliphatic hydrocarbons are given to you in Reference Table Q Homologous Series. have... a general formula and neighboring members differing by CH 2, with similar chemical properties and with a gradual change in physical properties. Trends in Boiling Points - Gradual increase in boiling point as the number of carbon atoms increases. Alkanes Alkanes are hydrocarbons that contain only single bonds. Alkanes are said to be saturated hydrocarbons Because their hydrogen content is at a maximum. Alkane general formula C n H 2n + 2 The names of alkanes all end in -ane. Methane butane are gases Pentane C 17 H 36 are liquids C 18 H 38 and higher are solids 15 Cycloalkanes (Not on Regent) Members of the cycloalkane group possess rings of carbon atoms. They have the general formula C n H 2n. Each carbon atom is bonded to a total of four carbon or hydrogen atoms. The smallest possible ring consists of cyclopropane, C 3 H 6. Alkenes Members of the alkene group have a double bond between two carbon atoms. One hydrogen atom has been removed from two adjacent carbon atoms, thereby allowing the two adjacent carbon atoms to form a double bond. General formula is C n H 2n Begins with ethene (ethylene) - C 2 H 4 3

4 Alkynes Members of the alkyne group have a triple bond between two carbon atoms. Two hydrogen atoms have been removed from each of two adjacent carbon atoms, thereby allowing the two adjacent carbon atoms to form a triple bond. General formula is C n H 2n-2 Begins with ethyne (acetylene) - C 2 H 2 Hydrocarbon Naming - Prefixes We use a series of prefixes to name hydrocarbons. The prefix relates to the number of carbon atoms in the longest chain of the hydrocarbon. This information is on Reference Table P. Table P + Table Q = All you need to know (if you know how to use them). 20 You Try Now! What is the molecular formula of Propane? What is the molecular formula of Propene? What is the molecular formula of Propyne? Naming Hydrocarbons 1. Is it an alkane, alkene or alkyne? The name must end with the proper suffix 2. How many carbons are in the longest chain? The name must begin with the proper prefix. 3. Is there a double bond or triple bond? We must put a number in front of the name that denotes where this bond is (which atom in the chain starts the bond). 4. Exception to #3: Molecules 3 carbons or shorter in length Organic Compound Nomenclature Naming Due to the large number, variety, and complexity of organic compounds, a consistent method of nomenclature has been developed. e IUPAC System of Nomenclature Compound is named as a derivative of the longest continuous chain of C atoms. Positions & names of the substituents added If necessary, substituents named alphabetically More than one of same type substituent di, tri, tetra The C atoms on the main chain are numbered so that the substituents get the smallest possible combination of numbers. Each substituent must have a number. 4

5 An Example to Consider The longest continuous chain of C atoms is five Therefore this compound is a pentane derivative with an attached methyl group Start numbering from end nearest the substituent The methyl group is in the #2 position The compound s name is 2-methylpentane. Substituents in Organic Compounds An Example Draw the structural formula for 2,3-dimethylhexane. Note that the end name is hexane. Draw a continuous chain of six carbon (C) atoms, with four bonds around each. An Example (cont.) Number the C atoms from right to left. Attach a methyl group (CH 3 --) to carbon number 2 and number 3. Add necessary H atoms. 2,3-dimethylhexane Confidence Exercise Draw the structural formula for 2,2,4-trimethylpentane. Note that the end name is pentane. Draw a continuous chain of five carbon (C) atoms, with four bonds around each. Confidence Exercise (cont.) Number the C atoms from right to left. Attach two methyl groups (CH 3 --) to carbon number 2 and one to number 4. 5

6 Confidence Exercise (cont.) 2,2,4-trimethylpentane Ball-and-Stick Model Add necessary H atoms. 2,2,4-trimethylpentane Name it! Name It! Name It! Name It!

7 Isomerism Isomers: Molecules with the same molecular formula, but with different structural formulas. No hydrocarbon smaller than butane has an isomer. After butane, the number increases exponentially. But Wait, That s Not All! There are a lot of ways of drawing Organic molecules. We can show each carbon and hydrogen bonded (structural formula): We can condense the bonds (condensed structural formula): Butane Isobutane We can get rid of the carbons in the chains all together, and focus on the geometry (skeleton diagram): And there s always space-filling! Or just focus on important things: Too many choices! I agree. What we will use in this class: Full structural formulas. Structural formula without hydrogens (only showing the bond, not the H) Condensed structural formulas. No skeletons! No Space Fillers Any Questions?