Chapter 3 Outline alkane hydrocarbon that only contains single bonds saturated a hydrocarbon is said to be saturated when it has the maximum number of bonded hydrogens another way to describe alkanes is saturated hydrocarbons methylene group CH2 a series of compounds like the unbranched alkanes that only differ by the number of CH2 groups are called a homologous series with each of the members themselves known as homologs butane is a homolog of propane IUPAC International Union of Pure and Applied Chemistry nomenclature 1 find the longest continuous chain of carbon atoms and use the name of this chain as the base name of the compound 2 Number the longest chain beginning with the end of the chain nearest a substituent 3 Name the substituent groups attached to the longest chain as alkyl groups Give the location of each alkyl group by the number of the main chain carbon atom to which it s attached 4 When 2 or more substituents are present list them in alphabetical order When 2 or more of the same alkyl substituent are present use the prefixes di tri tetra etc to avoid having to name the alkyl group twice Include a position number for each substituent even if it means repeating a number more than once degree of alkyl substitution the number of alkyl groups bonded to a carbon atom in a compound or in an alkyl group common uses for alkanes fuels solvents lubricants alkanes are hydrophobic meaning they are water hating and do not dissolve in water they re good lubricants and preservatives for metals because they keep water from reaching the metal surface and causing corrosion as alkane molecules increase in size unbranched their boiling point increases branched alkanes boil at lower temperatures than unbranched because branched alkanes are more compact with less surface area for London force interactions USES OF ALKANES C1 C2 gases at room temp difficult to liquefy usually handled as compressed gases After cooling they will liquefy though and liquefied natural gas mostly methane can be transported in special refrigerated tankers more easily than it can be transported as a compressed gas C3 C4 gases at room tem can be easily liquefied at room temp under modest pressure Stored in low pressure cylinders of liquefied petroleum gas LPG good fuels both for heating and for internal combustion engines Propane and butane have replaced Freons in aerosol cans because those Freons were said to damage the ozone layer C5 C8 free flowing volatile liquids primary constituents of gasoline Gas must be volatile and also resist the potentially damaging explosive combustion known as knocking Anti knock properties are rated by octane number that is assigned by comparing the gasoline to a mixture of n heptane which knocks badly and isooctane which isn t prone to knocking The octane number assigned to the gasoline is the percentage of isooctane in an isooctane heptane mixture that begins to knock at that same compression ratio C9 C16 higher boiling liquids that are somewhat viscous kerosene is the lowest boiling of all these fuels C16 and up most often used as lubricating and heating oils sometimes called mineral oils because they come from petroleum which was once considered a mineral paraffin wax is a purified mixture of high molecular weight alkanes with melting points above room temperature catalytic cracking converts less valuable fractions to more valuable products when cracking is done in the presence of hydrogen it s called hydrocracking cracking without hydrogen gives a mix of alkanes an alkenes natural gas is about 70 methane 10 ethane and 15 propane methane hydrate an ice like substance consisting of individual methane molecules trapped inside cages of water molecules paraffins another term for alkanes combustion rapid oxidation that takes place at high temperatures converting alkanes to carbon dioxide and water halogenation usually initiated by heat or light the reaction of alkanes with halogens in the presence of heat or light to give products with halogen atoms substituted for hydrogen atoms ETHANE CONFORMATIONS Newman projections a way of drawing a molecule looking straight down the bond connecting two carbon atoms Sawhorse structures dihedral angle the angle between the C H bonds on the front carbon atom and the C H bonds on the back carbon in the Newman projection eclipsed conformation staggered conformation lowest energy with the electron coulds in the C H bonds separated as much as possible anything between these 2 is a skew conformation as ethane rotates toward an eclipsed conformation its potential energy increases and there is resistance to the rotation resistance to twisting is called torsional strain and the energy required is called torsional energy conformational analysis the study of the energetics of different conformations BUTANE CONFORMATIONS totally eclipsed everything is right behind one another There are a lot more conformations draw here STUDY CONFORMATIONS steric strain higher alkanes gauche conformation make kinks in the zigzag structure we frequently draw alkane chains in this structure to represent the most stable arrangement cycloalkanes alkanes that contain rings of carbon atoms resemble the acyclic open chain alkanes in their physical properties and in their chemistry nonpolar cis having two similar groups directed toward the same face of a ring or double bond trans having two similar groups directed toward opposite faces of a ring or double bond geometric isomers cis trans isomers angle strain sometimes called Baeyer strain the strain associated with distorting bond angles to smaller or larger angles ring strain the extra strain associated with the cyclic structure of a compound as compared with a similar acylic compound composed of angle strain and torsional strain heat of combustion the amount of heat released when a compound is burned with an excess of oxygen in a sealed container called a bomb calorimeter torsional strain the resistance to twisting about a bond chair conformation the most stable conformation of cyclohexane with one part puckered upward and another part puckered downward boat conformation the less stable puckered conformation of cyclohexane with both parts puckered upward The most stable boat is the twist boat conformation twisting minimized torsional and steric strain axial bonds one of six three up and three down on the chair conformation of the cyclohexane ring that are parallel to the axis of the ring equatorial bonds one of the six bonds on