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Chemisty 123L exam study notes

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University of Waterloo
Carey Bissonnette

Experiment 1 A cis to trans conversionSaturday June 25 2005419 PM Notes on TheoryAlkenesoThey are hydrocarbons with a CC double bondDouble bonds are stronger and more reactive than single bondsoHydrocarbons with double bonds used to be known as olefins because they had an oily appearanceOleum means oilFicare means makeIsomersoGeometric isomers have the same molecular formula but a different geometric arrangementThey also have different physical propertiesoAlkenes exist as two different geometric isomersThis is because the double bond in an alkene cannot twist very much so there are two distinct geometric configurationsCis and transoThe two isomers are generally named cis and transCis means the same which is because the cis isomer will have some important molecular group on the same side of the molecule think about what C4H8 looks likeTrans means opposite so the important molecular groups will be on opposite sides of the moleculeooHeats of formation denoted as H are the change in heat for some system when a fmolecule is formedIf they are negative it means that heat is releasedmore heat is released when a reaction is more exothermicExothermic reactions happen naturally and thus their product is stableTrans alkenes are more stable than cis alkenes by about 1 kcalmole which means that their heats of formation are more negativeSteric hindranceoThis is when atoms or groups in a molecule are too close to each other and so there is repulsion between their electron cloudsoConsider cis2butene which has 2 CH3 groups on the same sideIf you measure the van der Waals radii the radius of an imaginary sphere surrounded the molecule for one CH3 group it is 2Aso if the two CH3 groups were as close together as possible but not touching their centers would be 4A apartHowever they are measured to be about 3A apartmeaning that they are too close to each otherHence the presence of steric hindranceoIn this lab we are investigating the interaction between the cis and trans isomers of 12ethylenedicarboxylic acidThe cis isomer is also known as maleic acidThe trans isomers is also known as fumaric acidHybridization of carbonosp3 hybridizationThis involves one 2s and three 2p orbitals do you know what an orbital is forming 4 sp3 orbitalsThe bonds between hybridized orbitals are called sigma bondsThe bonds between unhybridized orbitals are called pi bondsosp2 hybridization
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