Chapter 4 notesChapter 4 notesAlkanes- Hydrocarbons that lack pi bonds are called saturated hydrocarbons, or alkanes.- The names of these compounds end with the suffix “-ane”1. Methane2. Ethane3. Propane4. Butane5. Pentane6. Hexane7. Heptane8. Octane9. Nonane10. DecaneNomenclature of AlkanesStep 1: identify the longest chain (called the parent chain), if there is competition between two chains, then choose the one with the most number of substituents.Substituents: the groups connected to the parent chainStep 2: count the number of substituents, by numbering the carbons on the parent chain in order from either endStep 3: pick the group of substituents with the lowest number count.Naming substituents- They are named with the same terminology used for naming parents, only we add the letters “yl”. For example a CH3 group is called methyl and likewise for ethyl, propyl, butyl etc.- These substituents are called the alkyl groups- When the substituent is connected to a ring structure, the ring automatically becomes the parent- However this is true only if the ring structure has more carbons than any other part of the structureNaming Bicyclic compounds- Compounds that contain 2 fused rings are called bicyclic compounds- In the bicyclic systems, the term “bicycle” is introduced in the name of the parent.Ex. Bicyclohexane, Bicycloheptane etc.Steps:1. Identify bridge heads2. There are two different paths connecting these twobridge heads, so for each path count the number ofcarbon atoms excluding the bridgeheads themselves.- The path on the left of the bridge has only 2 carbons, the pathon the right of the bridge has 2 carbons and the bridge hasonly 1 carbon. - Hence after ordering the numbers from largest to smallest thecompound above is a Bicyclo [2.2.1] Heptane. 3. Numbering the parent: start on one of the bridge heads and begin numbering the longest path. - Since the compound above does not have a longest path, you can count towards any side in this case. So going from bridgehead “A” towards the right, and then counting the carbon on the bridge in the end, counts 7 carbons in total, hence the heptane. Constitutional IsomersEx.BA- Isomers are compounds with the same function, same molecular formula but different structures.- The image above shows 6 isomers of hexane (C6H14), of which two that are highlighted in green are the same isomers. This is determined using the IUPAC names of the two which sums up to 3-methylpentane. This is one way to avoid drawing the same isomer more than once. Drawing Newman projections- This is a way to show how molecules change their shape with timeConformations: Rotation of C – C bonds, allowing the a compound to adopt a variety of possible three dimensional shapes- Some conformations are higher in energy while others are low in energy.Newman Projection: used to compare the conformations of a molecule- The easiest way to obtain a Newman projection is going from wedges and dashes, then rotating them to a sawhorse depiction, then to a Newman projection using angular vision.- The way to look at it is best explained by this image, keeping in mind that the starting image is ofthe wedge and dash portrayal:Conformational analysis- There are two types of conformations:The staggered form (left) and theeclipsed form (right).- The hydrogen atoms are separatedfrom each other by 60⁰, this angle iscalled the dihedral angle/Torsionalangle.- The conformations are formed byrotating only one side of thecompound (in this case the one infront), keeping the back in its place. - As mentioned by the image the staggered form is the lowest energy form and the eclipsed is of the highest energy form.- The energies are shown in graphs using a constant sinusoidal graph with the eclipsed conformation being the peak while the staggered conformation is at the troughTorsional strain: is the difference in energy between staggered and eclipsed conformations.- Some conformations included having a methyl group instead of hydrogen groups and this changes the graphs for potential energy slightly and introduces us to a new type of energy conformation.Gauche interactions: the interaction between two methyl groups when they are next to each other in a staggered conformation.Gauche conformation: is the staggered conformation with the methyl groups being net to each other.- The diagram above shows a sinusoidal graph that is alternating, in other words it goes from low to high to low.- This graph sums up the difference in energy levels in the different gauche conformation, with theeclipsed version being the highest and the staggered form being the lowest of energies. Note that the farther apart the methyl groups are the lesser the gauche interaction.- Each interaction has energy associated with it and this table shows the ones that we need to know for now:Interaction Type of strain Energy cost (KJ/mol)H – H (eclipsed) Torsional 6H – CH3 (eclipsed) Torsional 6CH3 – CH3 (eclipsed) Torsional + steric hindrance 11CH3 – CH3 (Staggered/ Gauche)Steric hindrance 3.8- If incase, instead of the methyl – methyl interaction, there is a methyl – ethyl interaction, then the methyl – ethyl would have the bigger gauche interaction.- When determining the major and minor conformer using gauche interactions, keep in mind that the major conformer is the one with the lowest energy, hence in this case it’s the methyl – methyl interaction.Steric Hindrance: when atoms are brought to close together and if atoms are brought too close together,there is an associated cost in energy due to overlapping electron cloudsCycloalkanes- Are alkanes that in the form of closed shapes such as, triangles, squares, pentagons etc.- Cycloalkanes start from propane and move on.Cycloalkanes1. Cyclopropane - triangle2. Cyclobutane – quadrilateral 3. Cyclopentane - pentagon4. Cyclohexane - hexagon5. Cycloheptane - heptagon6. Cyclooctane - octagon7. Cyclononane – nonagon 8. Cyclodecane - decagon9. Cycloundecane – undecagon 10. Cyclododecane – dodecagon Conformations of Cyclohexane- There are two types of conformations that we will need to look at: chair conformer and a boat conformer.Drawing Axial and Equatorial positions- Each carbon in a cyclohexane ring can bear 2 substituents: one group occupies an axial position and the other group occupies an equatorial position.Axial position: is parallel to a vertical axis passing through the center of the ringEquatorial position: is positioned approximately