Lab Workshop 1: Nomenclature of alkane and cycloalkanes

Transcription

1 Lab Workshop 1: Nomenclature of alkane and cycloalkanes Each student work group choose a Leader (reads activity out loud, poses questions to group), Facilitator (makes sure everyone is participating equally, directs the conversation), Recorder (takes note on discussion, learned concepts and any conclusions), and Presenter (announces conclusions or presents activity to class). A. Nomenclature of Unbranched Alkanes (IUPA System International Union of Pure and Applied hemistry) Alkane = molecule consisting entirely of carbon and hydrogen atoms connected by single bonds. ritical Thinking Question (TQ): 1. ross out each molecule that is not an alkane l O 3 3 O 3 3 Memorization Task 1: Unbranched Alkanes NAME Structure # carbon atoms methane 1 ethane 33 2 propane butane 3(2)23 pentane 3(2)33 5 hexane 3(2)3 6 heptane 3(2)53 7 octane 3(2)63 8 nonane 3(2)73 9 decane 3(2)83 10 undecane 3(2)93 11 dodecane 3(2) tridecane 3(2) tetradecane 3(2)123 1 eicosane 3(2) ritical Thinking Questions: 2. Write the correct name of the unbranched alkane in TQ1. 3. What suffix do all the names of unbranched alkanes have in common?. What prefix stands for six carbons?

2 B. Nomenclature of anched Alkanes: Parent hain = longest continuous carbon chain found in a branched compound. Substituent = groups branching off the parent chain (side chain numbering always starts at the atom connected to the parent chain); Alkyl groups = substituent groups branching off the parent chain that consist entirely of carbon and hydrogen. locant = the carbon number where a group branches off the parent chain (used to indicate the location of a substituent) ritical Thinking Question (TQ): 5. ircle the parent chain in each molecule below and name the parent chain. 6. Number the parent chain to give the substituents the lowest number possible Parent chain = octane IUPA name = 2,5,6-trimethyloctane Memorization Task 2: ommonly found alkyl substituents NAME Structure methyl 3- # carbon atoms 1 ethyl 3-2 n-propyl 3-3 isopropyl n-butyl 3() 2- isobutyl 3 sec-butyl tert-butyl n-pentyl 3() 3-5 NOTE- If multiple different substituents exist on a parent chain, list them alphabetically, not including the di, tri, sec or tert prefixes (but iso is included when alphabetizing) 7. In the IUPA name in TQ6, what information do the numbers in the names convey? 8. What does the word tri indicate? 9. Give the IUPA names for the remaining two molecules above. 10. Explain what is wrong with each of the following names and correct each name: a.,-dimethylpentane b. 1,1,1-trimethylbutane c. 2,2-methylpentane d. 2-dimethylpentane e. 6-ethyl-2-methyl-pentyloctane

3 . Nomenclature of ylic Alkanes: If a ring is present in a molecule, the ring is almost always considered the parent chain. Use the word cyclo as a prefix before the alkane name to indicate it is a cyclic parent chain Number the carbons that bear substituents starting with one, and number around the ring towards the closest carbon that bears another substituent group to give all substituents lowest possible numbering. If there are two or more substituents, use alphabetical order to determine where to start numbering. ritical Thinking Question (TQ): 11. Give the correct IUPA name for the remaining three compounds below. 12. Draw the structures that correspond to the following names: a. 3-ethylheptane b. 1,1-diethylcyclopropane c. -sec-butyl-1-isobutyl-2-methylcylcohexane 13. Mono-substituted cycloalkanes do not include the 1 locant. Thus, 1-methylcyclohexane is inaccurate. Draw methylcyclohexane; explain why adding a locant does not add any new information. D. Nomenclature of Alkenes: Functional Group = the particular group of atoms in a molecule that primarily determines how the molecule will react. Alkyl halide = a hydrocarbon having at least one halide connected to a carbon atom. Alkene = a hydrocarbon having at least one double bond between carbon atoms. Alkyne = a hydrocarbon having at least one triple bond between carbon atoms. Alcohol = a hydrocarbon containing an O- functional group connected to a carbon atom that bears no other substituent but alkyl groups. The functional group(s) in a molecule usually determine the classification of that molecule and are indicated by suffixes in the name. The highest priority functional group determines its classification and lower priority functional groups often become substituents, indicated with prefixes. These will be learned slowly over the semester as we study each class of organic compounds. Rules for IUPA naming: Determine the parent chain (longest continuous chain or ring) of the molecule that includes the functional group of highest priority. Start numbering starting at the appropriate end of the parent chain (so important substituents have the lowest numbers). Number parent chain across a double or triple bond giving the bond lowest numbering unless an O group is present. Then it has highest priority and must be given lowest numbering. drop ane and add +ene for double bonds or +yne for triple bonds (double and triple bonds usually have the same priority, so number them to give the lowest numbering overall). Indicate location by the # of the first atom of the multiple bond or the # of the carbon to which the O is attached. Indicate the location and name of substituents as prefixes giving them lowest numbering possible, arrange alphabetically, and prefix with di, tri, tetra, if needed. alides are named as substituents and have the same priority as alkyl substituents, thus, are numbered and arranged alphabetically. Designate cis or trans or E or Z for double bonds when needed (we will learn this later).

4 Number cyclic cmpds so that 1 and 2 include the multiple bond if a double or triple bond is present. If an O group is present, then start numbering at the bearing the O and give the double bonded carbon atoms the lowest number possible. If treated as substituents, = and =- are called vinyl (or ethenyl) and allyl groups (or 2- propenyl), respectively. Side chains containing an alkene or alkyne are indicated as prefixes by dropping the e and adding yl like alkyl groups (ethenyl) or (3-butynyl) [ ----]. Always number the parent chain to give the functional group of highest priority the lowest number possible, before considering substituents. ritical Thinking Question (TQ), alkenes: methyl-1-pentene l 1. Why is the 1 locant needed in the name of the first compound above? 15. ow do you know that this compound has a double bond from its IUPA name? 16. What functional group class does it belong to? 17. Give the IUPA names to the remaining four compounds. E. Nomenclature of Alkene Stereoisomers (E/Z and trans/cis) Stereoisomer = compounds with the same molecular formula that differ only in the arrangement of their atoms in space. (Free rotation around double bonds cannot occur unless the double bond is broken and reformed.) (yclic alkenes of less than 7 carbons are always cis due to the size of the ring and do not have a cis prefix.) ritical Thinking Question (TQ): 18. Write the molecular formula for each of the compounds above. 19. Does the name 2-butene indicate which of the stereoisomers above is being referred to? 20. To indicate the difference between alkenes that have 2 substituents across a double bond, use the prefix trans (across the double bond relative to each other) or cis (same side of the double bond to each other). Thus, the correct IUPA names for the compounds above are cis-2-butene and trans-2- butene. 21. Add cis or trans where needed to the IUPA names in the alkene TQ question above. When more than 2 substituents exist around a double bond, cis and trans can no longer accurately describe the stereoisomers and a different systems is used, the ahn-ingold-prelog convention of E and Z. This system can also be used for alkenes with only 2 substituents. It will be discussed when we cover the chapter on Alkenes and Alkynes later in the semester.

5 F. Nomenclature of Alkynes (use IUPA rules indicated in Section D above): ritical Thinking Question (TQ), alkynes: 3-bromo--isopropyl-7-methyl-1-octen-5-yne l 22. alides are always substituents and are named by dropping the ine from the element name (bromine) and adding the letter o. list the substituent names of the following halides: F, l, and I. 23. Why is the parent chain numbered from left to right instead of right to left in the example above? 2. Why is the 5 locant placed in front of the -yne suffix, instead of by the 1 locant? (i.e., -isopropyl-3,7- dimethyl-1,5-octenyne)? 25. Note: the letter e is always dropped off the ene suffix before adding yne so that 2 vowels are not together if the locant is ignored. 26. Write the IUPA names for the remaining compounds above. G. Nomenclature of Alcohols: ritical Thinking Question (TQ), alcohols (use IUPA rules indicated in Section D above): O O 2,-cyclohexadienol O 27. Why doesn t the first alcohol above have a locant in front of the ol? 28. Should there be a locant in front of the other alcohol suffixes shown above? Why? 29. Write the IUPA names for the remaining compounds above. 30. Draw the following compounds: a. 2-methyl-2-heptene b. 5-butyl-6-isopropyl-5-decene c. 1,1,1-trifluoro-2-pentanol d. octa-1,3,5,7-tetrayne e. 1-chloro-2-(chloromethyl)cyclohexane f. 6-bromo-5-chlorocyclohex-2-enol Assignment Finish this packet if you did not do so in lab, and see the lab syllabus for additional information about this week s assignment.