Week 3 Chem 2030 Notes
Week 3 Chem 2030 Notes CHEM 2030 - 01
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CHEM 2030 - 01
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This 13 page Class Notes was uploaded by Shannon Z. on Saturday September 12, 2015. The Class Notes belongs to CHEM 2030 - 01 at University of Missouri - Columbia taught by Rainer Glaser in Fall 2015. Since its upload, it has received 39 views. For similar materials see Survey of Organic Chemistry in Chemistry at University of Missouri - Columbia.
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Date Created: 09/12/15
1 Alkane consist of chains of hydrocarbons 2 Sources of Alkanes a VIP natural sources i Petroleum 1 Liquid mixture containing many different organic compounds including alkanes andor cycloakandes ii Natural gas 1 Consists of methane 80 and ethane 510 and other higher alkanes 2 Associated with petroleum deposits a LPG Liquefied petroleum gas i Main component is propane ii Used in rural homes as a fuel source 3 There is about 1 million miles of natural gas pipe lines in the USA 4 When transporting natural gas it is liquefied because the liquid state is 3 Properties of Alkanes considerably more compact than the gaseous state a Insoluble in water i Water molecules are polar alkanes are nonpolar ii Water will not mix with alkanes iii Hydrogen Bonding 1 6 7 Water s high electronegativity makes it strongly polarized it is a strong polar covalent bond Water s strong polarization places a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom This ends up making the positive hydrogen atoms in a water molecule strongly attracted to the negative oxygen atoms in other water molecules Water molecules will line up with their hydrogen atoms facing the oxygen atoms because of this The hydrogen atoms are quite small and can get very close to the oxygen atoms This is called a hydrogen bond Hydrogen bonds can be very difficult to break iv The tight hydrogen bonds leave no room for the oils to mix in They don t want the oil to come in and mess up it s perfect configuration of hydrogen bonds but the oil wants in so that it can polarize v Instead the oil spreads out on top of the water in a thin film to achieve the most contact with the water via increasing surface area b Alkanes with nonpolar CH bonds do not mix well with water Plants use this inability to mix with water as a sort of waxy protective coat on their leaves and fruit c Alkanes have a lower boiling point than most other organic compounds thanks to van der Waals attractions vi vii viii xi xii Nonpolar molecules will on average equally share their electrons However the electrons are free to roam around the bond between the atoms At any given point in time they may be on opposite sides of the bond or both by one of the participating atoms When both electrons are at one side of the bond a temporary polarization is created 1 Called a fluctuating dipole moment The side with both electrons will have a partial positive charge The side with no electrons will have a partial negative charge When these temporary polarizations occur they can stimulate neighboring molecules to also temporarily polarize 1 Called an induced dipole moment The molecules partially positively charged sides will be attracted to other molecules partially negatively charged sides These interactions between temporarily polarized molecules are called van der Waals attractions Because these are weak attractions the molecules are easy to separate When converting a substance from a liquid to a gas with heat you re separating the hold molecules have on each other The higher the boiling point the stronger the bonds were Because van der Waal attractions have weak bonds they are easy to separate and thus have low boiling points 1 Alkanes whose molecules can come into contact with more molecules will have a higher boiling point a The more bonds you have to break the higher the boiling point Water and methane have similar masses but very different boiling points because water s strong hydrogen bonds keep it together 4 Alkane Conformations a Conformation different shapes a molecule can take by rotating around carbon bonds b Stereoisomers molecules that have the same connectivity but different spatial orientation c Staggered and Eclipsed Conformations Staggered 1 Bonds are offset so that none are parallel or line up with one another 2 Most stable conformation 3 Lowest potential energy 4 Maximizes space between bonds Eclipsed 1 Bonds are lined up so that they are parallel to one another 2 Least stable conformation 3 Highest potential energy d By rotating around carbon bonds you can change between staggered and eclipsed conformations 5 Nomenclature of Molecules Containing Halogens a On some alkanes there may be substituents that contain halogens b These halogens include fluorine chlorine bromide and iodide substituents c Procedure for naming iv vi vii viii Identify the longest chain and assign location numbers Make sure that the location numbers have been assigned so that the substituents are labeled with the lowest possible location number Identify the substituents 1 Halogens a Fluorine will be abbreviated as fluoro b Chlorine will be abbreviated as chloro c Bromide will be abbreviated as bromo Identify the location number that each halogen substituent is at Follow the number with a hyphen and the proper abbreviated name for that halogen substituent 1 If there are multiple halogen substituents use a comma to separate the different location numbers 2 If there are multiple substituents branching from one location number repeat that number as many times as there are branches a When labeling the substituent s name don t forget suffixes like di tri ect when there are more than one of that type of substituent After identifying halogen substituents separate them with a hyphen H from the location numbers of hydrocarbon substituents Label hydrocarbon substituents with the location number separated by commas Also write the location numbers and names of other substituents The substituent whose namecomes first alphabetically is listed first d Example r 3 aromall etrimethvlpenmwe l l I Me lll Me 6 Two new ways to draw structures a Sawhorse Single lines to represent bonds ii Junction of bonds represent a carbon iii An arrow to show direction of rotation iv eclipsed conformation staggered conformation b Newman Projection 7 Nomenclature and Conformation of Cycloalkanes a Cycloalkane i Rings of saturated hydrocarbons b Nomenclature i Prefix cyclo is placed before the alkane name corresponding to the number of carbons in the ring P 39 il he 1 quoth39 H l39 ffRH 939 fl an a 9 its Hun Aquot HE ILEI IanMail if H1 SF j i L5 quot39 KEEJIPIIJZIHJTEEIJ1L multilth Earle c3tllir1e1 ularrit cyt utmzanws WEI trul1t139ljau1i Eja tf l tmis ifiit ii Begin assigning location numbers by labeling the first substituent in alphabetical order as location number 1 iii If only one substituent is present you don t need to give the location number as it is assumed to be 1 iv Use commas to separate multiple location numbers for the same type of substituent v Separate the substituent s location number from it s name with a hyphen vi Give substituent name followed by cyclo insert what type of alkane it is H30 CH3 1 1dimethyloyelog vii Example L ii7propane c Conformation i A cycloalkane made of three carbons with attached hydrogen atoms is a cyclopropane 1 All of the carbons are planar in the same plane and are 60 from one another 2 The hydrogens are eclipsed above and below the plane of the carbons ii Cyclopropane is the only cycloalkane with all of the carbons in the same plane The others are puckered and make a zigzag circle of carbons iii Cyclohexanes are very common in nature Diamonds are full of cyclohexanes 1 Their most favorable conformation is the chair conformation n u a u 11 b All of the angles between carbons are 1095 c All of the hydrogen atoms are perfectly staggered i The hydrogen atoms that lie above or below the plane of each of the carbons are said to be axial 1 In cyclohexane s chair conformation there are 6 axial hydrogen atoms three above and three below each of the carbon s plane ii The hydrogens that lie in the plane of each of the carbons are said to be equatorial 1 In cyclohexane s chair conformation there are 6 equatorial hydrogen atoms d By rotating around carbon bonds you can flip the chair conformation backwards i This causes the axial hydrogens from cyclohexane s original orientation to become equatorial Likewise the original equatorial hydrogens will become axial e The carbon bonds are always rotating As temperature rises the rotating around carbons bonds speeds up 2 When a substituent is added to cyclohexane it will prefer to be orientated equatorially 3 There is another conformation for cyclohexanes but it is less favorable It is called the boat conformation H a H H 8 CisTrans somerism in Cycloalkanes a Cistrans isomerism is also known as geometric isomerism b Cis somerism i Used to refer to when the substituents on a cycloalkane are all orientated either above or below the plane of the carbons in the cycloalkane ii Not as energetically favorable as it does not maximize the distance between atoms c Trans somerism i Used to refer to when the substituents on a cycloalkane are orientated both above and below the plane of the carbons in the cycloalkane d lmage from text page 54 i Left figure 1 Note how the substituents in blue are both above the plane of the carbon ring 2 This is an example of cis isomerism ii Right figure 1 Note how one of the substituents in blue text is above in the plane of the carbon ring and one is below the plane of the carbon ring 2 This is an example of trans isomerism e You cannot rotate between cis and trans isomers by simply rotating carbon bonds Instead it would have to break the subtituent off of the carbon ring and switch places with one of the H atoms on that particular carbon ring atom i When you have to break bonds to form an isomer those isomers are called configurational isomers ii Isomers created by rotating bonds are called conformers 9 Alkane Reactions a Because alkanes have single nonpolar covalent bonds they do not react well with other stuff i Alkanes do not react with most common bases acids oxidizing agents or reducing agents ii Alkanes do react with molecular oxygen and halogens b Oxidation and Combustion i When given enough oxygen alkanes will burn producing water and carbon dioxide ii This burning is called combustion and is a exothermic reaction meaning that it releases heat 1 These exothermic reactions are the basis behind using natural gas for a heat source iii All you need to initiate the reaction is a spark iv Combustion replaces CH bonds with CO bonds making it an oxidation reaction v There are partial and complete oxidation reactions 1 Complete a There is enough oxygen present to completely react with all of the available carbon and create as many CO bonds as possible 2 Partial a There is not enough oxygen present to completely react with all of the carbon and there will only a fraction of the possible CO bonds will be formed 3 The more CO bonds the more oxidized something is vi Combustion of Methane 1 Partial and complete combustions Know the top three mmplieie 2 E114 4 GE 2 CUE 4 H20 2 Ell 3 GE E C 11 H20 2 EM 2 GE E C 4 H20 2 115 2 GE 2 H200 2 Hat 2 EHamp 3 oz 2 2 HEB vii Jr L III I H imlouo H a CO carbon monoxide Harmful to people 02 a diradical has two radical oxygen atoms can react with methane in a combustion reaction as well 3 II c Halogenation of Alkanes When halogens and alkanes are exposed to sunlight or heat they will react to one another This is an exothermic reaction One or more of the alkane s hydrogen atoms will be replaced with a halogen atom 1 These kinds of reactions when one atom is replaced with another kind of atom are called substitute reactions If there are enough halogens present substitute reactions will continue until all of the carbon atoms are saturated with halogens v Substitute reactions can occur in short or long chains if hydrocarbons vi Three steps 1 Initiation a The halogen molecule is broken up making the atoms from that molecule new radicals 1 tit ligh t if if initiation 3 Ell 39 Cl 3 7 Cl quot l 1E1 quot Make m hem new rad ta chlorine nimilecule clfilorijne atoms 2 Propagation a The new radicals steal a hydrogen atom from an alkane and bond with it leaving the alkane a radical because it now has an unpaired electron lite H C31 Hi iii L 39 allay propagation 5 radical Number of mig gf l Ra cl Cl 39R l rel Radical induced humanism twirl mwide 3 Termination a The radical alkane bonds with radical halogens reducing the amount of radicals f eCl Cll termination i Rial PEER RE Raicale leappeair 1511 a R 61 b vii The primary two halogens alkanes will react with are chlorine and bromide 1 Reactions with chloride are called chlorination a Methane and chlorine i The Cl2 bond is broken leaving radical chlorines that want to fulfill their octets ii The CI radical rips off one of methane s hydrogens and takes it s place iii The image shows chlorination of methane The bottom row shows all of the different ways that chlorine can bond what s left of the methane It can form CH3CI CHZCIZ CHCI3 and CCI4 and varying numbers of HCl molecules iv Know both the traditional black and proper blue names for these molecules mulluh CH4 l Il IHII HC I L mcllmnc tnlnrmnviham methyl chloride hp 242 r 1 ii l lll gt thl HLI gt l mthlumnu39llmm39 trnhlurmmzhain39 l1 lquothlllHl39HlllL ll ldllL39 HCI limlhylcm chloride chloroform carbon lclrMhloridc hp m hp m 7 Z hp 765 t b Propane and Chlorine i The Cl2 bond is broken leaving radical chlorines that want to fulfill their octets ii The CI radical rips off one of propane hydrogens and takes it s place iii The image shows all of the different ways that chlorine can bond what s left of the propane EHJEHELEIUE 7 Cl lg CHgCHi l Hallili sHLlig fir HIE HI TERI C propane icltllnmpmpane Euclilnmpmjmne iiipr HII clturde fisoprtig tl chloride iv Know both the traditional black and proper blue names for these molecules 2 Reactions with bromide are called bromination a Light or heat breaks up a Br2 molecule The bromides now want to fulfill their octet and do so by removing a hydrogen atom from a hydrocarbon One bromine atom will take the hydrogen s place and the other will bond with that hydrogen 10 Primary Tertiary and Secondary Hydrogen atoms a Primary i Hydrogen atoms that are attached to a carbon Of the four saturated bonds that carbon could make only one will be to another carbon atom Primary Hydrogens In Butane H l l ii Primary hydrogen atoms are circled above in red b Secondary i Hydrogen atoms that are attached to a carbon Of the four saturated bonds that carbon could make only two will be to another carbon atom l l 39l it quotC J l i T i El H EH3 H c Tertiary i Hydrogen atoms that are attached to a carbon Of the four saturated bonds that carbon could make three will be to another carbon atom l l l H IL E a C Jtli T CHE on H CH H 11 Misc a Hydrogen bonding and van der Waals attractions are types of nonbonding intermolecular interactions b To find the number of H or C in a normal alkane you used the formula CnH2n2 where nnumber of carbons c To find the number of H or C in a cycloalkane use the formula CnHzn where nnumber of carbons d Helpful flow chart for identifying types of isomers Images httpscienceuvueduochemindexphpalphabeticaIabboatconformation httpwwwintroorganicchemistrvcomcvcichtmckattempt1 Lecture Slides Textbook httpscienceuvueduochemindexphpalphabeticaIcdconformation httpwwwsidesharenetDenisoanarkahfreeradicaIsubstitutionofpropanean unanswerabIecapequestion httpwwwchemuclaeduhardingIGOCSsecondarv hvdrogenhtm httpwwwchemuclaeduhardingIGOCTtertiarv hvdrogenhtm