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NCSU CH 220 - Alkenes

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CH 220 1st Edition Lecture 7 Outline of Current Lecture I. AlkenesII. Naming alkenesIII. Naming cycloalkenesIV. Common namesV. Cis-Trans isomerism in AlkenesVI. E,Z systemCurrent Lecture I. Alkenesa. Any hydrocarbon that contains a carbon-carbon double bond is an alkeneb. Many naturally occurring materials are classified as alkenesi. Ethyleneii. alpha-Pinene – the fragrance of pine, pine-soliii. beta-Carotene – orange pigment and vitamin A precursorc. Common in industrial preparationi. Many products are composed of ethene1. Polyethylene – common plastic2. Vinyl chloride – pvc pipeii. Propene1. Polypropylene – carpet fibersII. Naming alkenesa. Name the parent hydrocarbon i. Must include the double bond in the parent, it cannot be in a substituentb. Number the carbons in the chain – making sure that the double bond gets the lowest number possible (it takes precedence over all substituent numbering)c. Write the full name, numbering substituents accordingly i. Position in chainii. Alphabetically2-hexene 2-methyl-3-hexeneIII. Naming cycloalkenesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Lecture 7 a. Bars represent bonded pairsb. Dots represent lone valence electrons that are non-bondingc. Methane is the smallest organic moleculed. Examples of the amount of bonds and lone pairs are shown below:1-methylcyclohexene Don’t need to put a 1 before the cyclohexane because it presumes that the double bond begins on number 1Since we must number through the double bond (i.e. one end of the double bond is #1, the other is #2) and we must give the closest substituent to the double bond the lowest possible number, the name of this cycloalkene is 1,5-dimethylcyclopentene.IV. Common namesa. Some ethenes have common names that have been used for a long time, however IUPAC accept some as accepted names and some as unaccepted namesFor that reason, it is best to use the IUPAC nameExamples:IUPAC Name Common NameEthene EthylenePropene Propylene2-methylpropene Isobutylene2-methyl-1,3-butadiene IsopreneV. Cis-Trans isomerism in Alkenesa. Alkenes might have the same formula, but can be can have different names and properties because they are stereoisomersThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. CH 220 1st EditionLecture 7 b. Stereoisomers are connected in the same manner, but have a different spatial arrangement which results in different biological compoundsc. A double bond doesn’t lend itself well to rotating – the  bond is prohibitive – it would need to be broken to rotate, whereas  bondsVI. E,Z systema. Method for naming alkenes that have bonds to more than one type of substituents b. Need to figure out the higher priority groups on either side of the line (as shown below) – rules will follow further down the pagec. If the higher priority substituent from each side point in the same direction (like Br & Cl are doing, above) then it is named with a (Z)- at the beginning of the name. (“On zee same side”)d. If the higher priority substituent from each side point in opposite directions, thenis it names with a (E)- at the beginning of the name. e. Rule 1 – Must rank atoms that are connected – the higher atomic number gets higher priority.f. Rule 2 – if atomic numbers are the same, compare at next connection point (i.e. if you are comparing 2 carbons, what are they connected to? What are the atomic masses of those atoms?These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. CH 220 1st EditionLecture 7 By using rule 2, we can deduce that the CH2-CH3 would take priority, because even though the bond is made to the carbon for each of the two bonds, the lower carbon is connected to 1 x carbon and 2 x hydrogens, which have a higher mass than the 3 x hydrogens that the upper carbon is connected to.g. Rule 3 – Multiple bonded atoms are equivalent to same number of single bondedatoms – for instance if you have a carbon double bonded to an oxygen, that would be counted as being two separate bonds. h. After naming either (Z)- or (E)-, we must then find the longest chain (parent chain) and name it, find the substituents, number the carbons and write the name.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. CH 220 1st


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