Hydrocarbons Objectives Describe the bonding in hydrocarbons. Distinguish between straight-chain alkaneand branched-chain alkane.
Organic Chemistry• Includes the Chemistry of • Carbon compounds number virtually all carbon more than a million, with compounds, regardless of many valuable properties: their origin. • One main reason is carbon´s• Before scientists believed unique bonding ability. that organic compounds could only be sinthesized by • The simplest of the organic organisms, but Friedrich compounds are the Wöhler(1800-1882) refuted Hydrocarbons . that theory in 1828.
Basic Principle of Carbon Bonding:• Carbon has four (4) valence electrons, therefore will always form four covalent carbon- hydrogen bonds.Note: Remembering this will help you complete and correct structures for organic molecules.
Types of Formulas:• Structural Formulas: Convenient to write. Two-dimensional representations of three-dimensional molecules
Carbon has the ability to make stable carbon-carbon bonds and to form chains. This is the main reason for the numerous carbon compounds. Carbon + Hydrogen→ Methane C + H2 CH4
Straight-Chain Alkanes:• Contain any number of carbon atoms, one after the other, in a chain• They always end in –ane• To draw the structural formula for a straight-chain alkane, write the symbol for carbon as many times as necessary to get the proper chain length.• Then, fill in with hydrogens and lines representing covalent bonds. – Each covalent bond is equivalent to two electrons.
Homologous Series:The straight chain of alkanes are an example ofa homologous series. A group of compounds form a homologous series if there is a constant increase/increment of change in molecular structure from one compound in the series to the next.The -CH2- group is the increment of change instraight –chain alkanes.As the number of carbons in the straight-chainalkane increases, so does the boiling point andtheir melting point.
• Molecular Formula:• CH4 Methane • Complete Structural Formulas:• Show all the atoms and bonds in a molecule. Complete Structural Formula • Condensed Structural Formulas:• Leave out some bonds and/or atoms from the structural formula. Although they do not appear, you must understand that these bonds and atoms are Condensed Structural Formula there.
Nomenclature/ Naming System: IUPAC: International Union of Pure and AppliedChemistry. All the names end in –ane. The root part of an alkane´s name indicates how many carbon atoms it contains.Scientists also rely on a combination of systematic,semisystematic, and common names to identify organiccompounds. Some organic compounds are best known for theircommon names.
Branched-Chain Alkanes• An alkane with one or more alkyl groups – An alkyl group is a hydrocarbon substituent • Substituent: an atom or group of atoms that can take the place of a hydrogen atom on a parent hydrocarbon molecule. – An alkyl group consists on an alkane with one hydrogen removed. – Sometimes referred to as radicals. – Change the suffix –ane from the parent structure to -yl
Rules for Naming Branched-Chain Alkanes:1. Find the longest chain of carbons in the molecule. We consider this the parent structure.2. Number the carbons in the main chain sequence. Start at the end thatwill give the groups attached to the chain the smallest numbers.3. Add numbers to the names of the substituent groups to identify theirpositions on the chain. These numbers become prefixes to the name ofthe parent alkane.4. Use prefixes to indicate the appearance of a group more than once inthe structure. Ex. Di-, tri-, tetra-; penta-, etc.5. List the names of the alkyl substituents in alphabetical order.6. Use proper punctuation. Commas( ,) are used to separate numbers,hyphens(-) are used to separate numbers and words. The entire name iswritten without spaces.
To draw the formula when given the name:• With an alkane name and knowledge of the IUPAC rules, it is easy to reconstruct the structural formula.• Steps:1. Find the root word(ending in –ane) in the hydrocarbon name.2. Number the carbons on this parent chain.3. Identify the substituent groups. Attach the substituents to the numbered parent chain at the proper positions.4. Add hydrogens as needed.
Other Properties of Alkanes:-They are non-polar-Hydrocarbons of low molar mass tend to begases or low-boiling liquids.-Non-polar organic molecules are insoluble inwater.-Rule: “Like dissolves like” -Polar dissolves polar and non-polar dissolves non-polar. - Non-polar will never mix with a polar.
Practice Problems: Name the following compounds
Unsaturated Hydrocarbons: Objectives:• Explain the difference between unsaturated and saturated hydrocarbons.• Differentiate between the structures of alkenes and alkynes.
Alkenes• Alkanes are said to be saturated compounds because they contain a maximum number of hydrogens.• Alkenes and alkynes, on the other hand, contain double and triple bonds respectively.• They are said to be unsaturated compounds because they contain fewer number of hydrogens in their structure.
IUPAC Naming System for Alkenes:1. Find the longest chain in the molecule that contains the double bond. This is the parent alkene. As a base, you use the base name of alkanes and change the suffix –ane to –ene.2. The chain is numbered in the same way that alkanes, except that the carbon atoms of the double bond get the lowest possible numbers.3. Substituents on the chain are named and numbered in the same way they are for alkanes. Ethene and propene are the simplest alkenes.
Alkynes:• Are hydrocarbons containing carbon- carbon triple covalent bonds• They are unsaturated compounds• They are not plentiful in nature• The simplest alkynes are: ethyne, propyne, butyn e• Ethyne is commonly called acetylene.