Alkenes and Alkynes Week 4
Alkenes and Alkynes Week 4 CHEM 2030 - 01
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This 7 page Class Notes was uploaded by Shannon Z. on Tuesday September 29, 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 33 views. For similar materials see Survey of Organic Chemistry in Chemistry at University of Missouri - Columbia.
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Date Created: 09/29/15
Alkenes and Alkynes Chapter 3 1 Hydrocarbons with CC double bonds are alkenes Hydrocarbons with CC triple bonds are alkynes 3 You can turn and alkyne or alkyne into an alkane by adding hydrogen atoms increasing the amount of electrons present in the molecule and removing the need for the carbon atoms to form multiple bonds a You only need to add one hydrogen atom for each double bond in an alkene to turn it into an alkane i This means that alkene double bonds are 1 unsaturated b You only need to add two hydrogen atoms for each triple bond in an alkyne to turn it into an alkane i This means that alkyne double bonds are 2 unsaturated H2 acazcaa W catalyst alkane GHECHER 39 R Hill alkane I aatalyat alkane 4 Multiple double and triple bonds a Compounds with two double or triple bonds are called alkadienes or dienes b Compounds with three double or triple bonds are called trienes c Compounds with many double or triple bonds are called polyenes 5 Cumulated Conjugated and Nonconjugated Polyene Connectivity a Another means of classification b Cumulated i When there is a pattern in the bonds between carbons so that double bonds are lined up one after another c Conjugated i When there is a pattern in the bonds between carbons so that there are alternating single bonds with multiple bonds ii There is only one bond between the multiple bonds d Nonconjugated i Also called isolated ii When multiple bonds are separated by two or more single bonds ElliTES Culmlullated Conjugated Isolated C ZCZE CZC CZS CZ C C CZC CCCC CCEEEC CECCCCEC titlmulal E jtg led I i t unjtlgateu i ollaletljl 6 Features of a Double Bond a Double bonds are trigonal i Atoms in a double bond are only attached to three other atoms not four This makes them trigonal b Planar i The carbons in a CC double bond are planar to each other as well as the atoms attached to those carbon atoms 1 Figure 31 Page 73 in text c Rotation around double bonds is restricted d Double bonds are shorter than single bonds i Triple bonds are shorter than double bonds 7 Orbital Models of Double Bond using Carbon as an example a There is a 120 angle between orbitals b Individual atoms i Three orbitals will be planar a These three orbitals are sp2 hybridized b They have one full 2s orbital and one partial 2p2 orbital c The sp2 orbitals each contain one of the carbon s valance electrons ii One orbital is perpendicular to these sp2 orbitals 1 This is a p orbital 2 The p orbital contains one of carbon s valance electrons a Note these electrons are held more weakly by the atom than the sp2 orbital s electrons This makes them vulnerable c When two carbon atoms form a double bond i One of each of the carbon s sp2 orbitals will bond creating a sigma bond between the two ii Each of the carbon s p orbitals will bond creating a pi bond iii There is a total of one sigma and one pi bond between the two carbon atoms 8 Electrophiles and Nucleophiles a So the electrons in the p orbital are vulnerable to attack by other atoms They can be taken away b Electrophile i An atom or compound that really wants electrons ii Often cations positively charged c Nucleophile i Electron rich atoms or compounds They have extra electrons and will donate them to electrophiles ii Doubly bonded carbons are nucleophiles d Electrophilic Addition Reactions i You have a double CC bond ii A hydrogen atom is approaching iii The nucleophile is the carbon and the electrophile is the hydrogen atom iv This is where it gets confusing so be careful and read slowly v The hydrogen approaches the pi bond formed by the two carbons vi The hydrogen proton uses both of the electrons in the pi bond to bond to one of the carbon atoms 1 To reiterate Both electrons from the CC p orbitals are being uses to tie the hydrogen to only one of those carbon atoms vii The carbon that is not bonded to the hydrogen is now missing an electron and is considered is a carbocation viii Carbocations are extremely reactive ix These reactions can also happen with chlorine and bromine H C C X carbocatmn 9 CisTrans smerism 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 substituent 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 10 Nomenclature of Alkenes and Alkynes a Assign location numbers i Make sure that you assign the location numbers so that the location number for multiple bonds and substituents is minimized ii Of this multiple bonds take priority begin the numbering closest to the multiple bonds rather than closest to the substituent iii The longest chain MUST contain the multiple bond Multiple bonds cannot lead to substituents Cl i C mi iIZ J39Ci C t a l 1 iv L 1 b If it is a cis or trans structure indicate so by writing cis or trans first followed by a hyphen c Write the location numbers of substituents separated by a comma and followed by a hyphen Write the name of the substituents with the appropriate numerical prefix Another hyphen f Write the location numbers of multiple bonds separated by a comma and followed by a hyphen g If the molecule contains a ring of carbons write the prefix cyclo h Write the name of the root molecule with the appropriate suffix i Suffixes 1 Double bond a 1 double bond end with ene b 2 double bonds end with diene 2 Triple bond a 1 triple bond end with diyene 3 Double and triple bonds a End with enynes i for alkanes and alkenes is mostly the same only you change the suffix on the carbon chain s name to ene or yne as needed 11 Reactions a Addition Reactions i Most common type of alkene reaction ii You simply add atoms to remove double bonds iii Example 1 You have a two carbon atoms that are joined by a double bond 2 You have a molecule which we will call AB 3 A and B s bond is broken and they each bond with one of the carbon atoms breaking double bond and leaving them saturated 4 The end product has no pi bonds just saturated sigma bonds lbrealk lbrealk f rlm m lboinldl glboinldl 39lb lnldls V l i iv b Halogenation i Alkenes can add chlorine and bromine to themselves ii Like a normal addition reaction this will nullify a alkene s double bonds iii The only difference is that you are adding bromine and chlorine EH CEl 1Eltl1 CH Cltl 1 Br 6 Elli E131 quotijlll 39EL IE E lt13 iv Er EHquot Eur Br 1 Adding bromine to a compound can indicate whether or not it is saturated a Make sure both the bromine and compound are liquid b Bromine is brown c Add the bromine i No color change the compound is saturated ii Compounds turns brown the compound is unsaturated c Hydration i Adding water to an alkene ii Water can be bonded to an alkene if an acid catalyst is present iii The water will be divided into two compounds an H and an OH group Each will bind separately to the alkene iv The result is an alcohol V H UH 12 More molecules whose names you need to know Emma CHEECHE mam ethane E39t hE E ethjme propane F FDFIEEIE pr pyn Ethylene acetylene propylene ethane ethyne propane vinyl vinyl Eil39ll l39iii 39 ethanle lichll r ethmel E 3939 39 E 3939 allyl lily chloride 2 pmpenyl Ebchlompmpewei a 13 Geometry of Alkynes and Alkenes a The more bonds that are present the shorter the bond length i CC single bond length 154 A ii CC double bond length 134 A b Rotations of alkenes and alkynes is restricted c Bond angles Bond angles between single bonds are smaller