Alcohols of Pharmaceutical Importance – PST05106 Pharmaceutical Organic Chemistry
NTA Level 5 • Semester 1 • PST05106 Alcohols of Pharmaceutical Importance Pharmaceutical Organic Chemistry • Source Session/Topic 11 Full source-text version: all educational wording from the extracted learning source is retained; only presenter/tutor metadata and web-layout noise are removed, while formatting is improved for readability. Session 11: Alcohols of Pharmaceutical Importance. Total Session Time: 120 minutes Prerequisites None Learning Tasks By the end of this session students are expected to be able to: • Define alcohols • List alcohols and their isomers • Explain nomenclature of alcohols • Draw chemical structure of alcohols • List chemical properties of alcohols • Explain chemical reactions of alcohols Resources Needed: • Flip charts, marker pens, and masking tape. • Black/white board and chalk/whiteboard markers. SESSION OVERVIEW |Step |Time |Activity/ |Content | | | |Method | | |1 |05 minutes |Presentation |Introduction, Learning Tasks | |2 |10 minutes |Brainstorming |Definition of Alcohols | | | |Presentation | | |3 |15 minutes |Presentation |Alcohols and their Isomers | |4 |15 minutes |Presentation |Nomenclature of Alcohols | |5 |15 minutes |Presentation |Chemical Structure of Alcohols | |6 |15 minutes |Presentation |Chemical Properties of Alcohols | | | |Buzzing | | |7 |35 minutes |Group |Chemical Reactions involving | | | |discussion |Alcohols | | | |Presentation | | |8 |05 minutes |Presentation |Key Points | |9 |05 minutes |Presentation |Evaluation | SESSION CONTENTS. STEP 1: Presentation of Session Title and Learning Tasks (5 minutes) READ or ASK students to read the learning tasks and clarify ASK students if they have any questions before continuing. STEP 2: Definition of Alcohols (10 minutes). |Activity: Brainstorming (5 minutes) | | | |Ask students to brainstorm on the following question: | | | |What are Alcohols? | | | |ALLOW few students to respond. | | | |WRITE their responses on the flip chart/ board. | | | |CLARIFY and SUMMARISE by using the content below | • Alcohols are a family of organic compounds containing a hydroxyl (OH) group bonded to an sp3 hybridized carbon atom. • The general formula is CnH(2n+1)OH or R-OH. • Alcohols are named in similar manner as in alkenes except that the suffix –e from alkanes is replace by –ol. • Alcohols are classified into three groups: primary, secondary, and tertiary, depending on the carbon atom bonded to the – OH group. • If the carbon atom is primary (bonded to one other carbon atom), the compound is a primary alcohol. • If the OH group is attached to a carbon atom that is joined to two other carbon atoms, it is a secondary alcohol, and the carbon atom to which it is attached is a secondary carbon atom. • If the OH group is attached to a carbon atom that is joined to three other carbon atoms, it is a tertiary alcohol, and the carbon atom to which it is attached is a tertiary carbon atom. Primary alcohols [pic] [pic] [pic] STEP 3: Alcohols and their Isomers (15 Minutes). • Alcohols exhibit following three types of isomerism. o Chain isomerism. o Position isomerism. o Functional isomerism. Chain isomerism • Alcohols containing at least 4-carbon atoms form chain isomerism due to the different structure of C-skeleton in the longest chain. [pic] Position isomerism • Alcohols containing at least 3 C atoms form position isomerism due to a different position of a hydroxyl group (OH). Example [pic] Functional isomer • Alcohols containing at least 2 carbon atoms give functional isomers. The functional isomer of an alcohol is ether. Example [pic] STEP 4: Nomenclature of Alcohols (15 minutes). • The IUPAC system provides unique names for alcohols, based on rules that are similar to those for other classes of compounds. • In general, the name carries the -ol suffix, together with a number to give the location of the hydroxyl group Rules 1. Select the longest continuous carbon atom chain containing the carbinol (hydroxyl) group(s). 2. Number the chain, giving the hydroxyl (alcohol) substituent(s) the lowest number possible. 3. Name the longest chain as an alkane, but drop the terminal -e and add -ol. Ethane would become ethanol. 4. For monohydric alcohols the letter ‘-e’ at the end of the root name is replaced by the ending ‘-ol’ with a number, when necessary, to show the position of the –OH group on the carbon skeleton. [pic] 5. If more than one hydroxyl group is present (for polyols i.e. dihydric,trihydric etc.) the name becomes -diol, -triol, etc. and the terminal -e in the parent name is not dropped from the alkane name. But the letters ‘diol’ ‘triol’ etc & numbers 1,2,3 etc are added to the ending to show how many –OH groups & their position • For example ethane with two hydroxyl groups would become ethanediol. • Since the hydroxyl groups could be on or different carbon atoms, one needs to specify where the hydroxyl groups are attached. • The name would be 1,2-ethanediol if the hydroxyl groups are on adjacent (vicinal) carbon atoms. • Updated nomenclature rules suggest that the position of substituent attachment should precede the functional group name, e.g., ethane-1,2- diol rather than 1,2-ethanediol. 6. Indicate by numbers the positions of other groups attached to the parent chain • OH group takes priority (even over -ene or -yne) [pic] • Considering the example below: [pic] • The complete IUPAC name is 1-bromo-3,3-dimethyl-2-butanol. • The new IUPAC positioning of numbers would place the 2 next to the group it locates (-ol), giving the name 1-bromo-3,3-dimethylbutan-2- ol. 7. Cyclic alcohols are named using the prefix cyclo-; the hydroxyl group is assumed to be on carbon number 1, C1. [pic] [pic] STEP 5: Chemical Structure of Alcohols (15 minutes). • Alcohols fall into different classes depending on how the -OH group is positioned on the chain of carbon atoms. There are some chemical differences between the various types. Primary alcohols • In a primary (1°) alcohol, the carbon atom that carries the -OH group is only attached to one alkyl group. Some examples of