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5. Alcohols, Ethers and Thiols- Orgo.docx

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Western University
Chemistry 1027A/B
Mel Usselman

Organic Chemistry October 24, 2012 5. Alcohols, Ethers and Thiols Structure and Nomenclature - Alcohols have general formula R-OH - O atom is always ignored in the calculations of units of unsaturation o Oxygen is zero when doing calculations for unsaturation - O is sp3 hybridized o 2 sp3 orbitals occupied by lone pairs - Thiols are alcohols where sulfurs has replaced an oxygen - S is also always ignored in calculations of unit of unsaturation - When naming alcohols- OH take priority over the pi bonds - Alcohols are classified as primary secondary and tertiary depending on the sp3 carbon atom Physical Properties - Is the C=O polar? o Yes - The oxygen has lone pairs on it meaning it can function as a base - The hydrogen can function as an acid - Look at what circumstances it acts as an acid and what circumstances it acts as a base - Polarity is less in thiols because it is less electronegative than O o Other then than everything else is the same as alcohols - Hydrogen bond is more like an ionic bond attraction of opposite electron charges - Alcohols have a high boiling point for their size - OH groups greatly increase the solubility of organic molecules in water - Water molecules stick together - At any food ingredient, any vitamin- if you see lots of OH on it (ex. Glucose) this compound is soluble in water- nature has made the compound to be this way - Most noteworthy feature of thiols is that they smell terrible Chemical Reactions of Alcohols and Thiols - Hydration of alkenes - Substitution of alkyl halides - (1) Acid and Base Reactions o **Make sure you can link things together from the first midterm material and the new stuff- will help you understand the material better ** o Take an alcohol but it in a strong base it will protonate the alcohol o Take an alcohol and put it in a strong acid and it will take off the H of an alcohol o ROH + NA  RO(-)Na(-) + 1/2H2 October 26, 2012 - Should know what makes an acid- things that are able to loose a hydrogen - There are molecule that are distinctly acids and other molecules that are distinctly bases - ROH – this is polarized  they hydrogen here is fairly acidic - ROH- bumps into another solution that is highly acidic and has a low pH it will accept a hydrogen molecule 2. Conversion to Alkyl Halides - Alcohols are converted to alkyl halides by substitution - C-OH + X  C-X o Can proceed by an SN1 or an SN2 mechanism - Major way to do this is to treat the alcohol with a major halogen atoms o Tertiary alcohols react by an SN1 mechanism but only after the hydroxyl group is protonated - In the presence of a strong acid (like HX) hydrogen protonates the OH to OH2 o Once you protonate an OH and was once an okay leaving group, once you protonate it becomes and excellent leaving group - Primary and secondary alcohols also give alkyl halides on reaction with HX o If dealing with hydroxyl on a primary carbon- the primary carbocation does not want to form so the OH2 will NOT leave on its own - When you do the reaction with a primary carbon you are not going to get 100% yield in these reactions - Reactions with Thionyl chloride, SOCl2 o Does what HCL does o Will substitute OH with a chlorine o Will do it for primary and secondary only o Primary and secondaries will do it well- not tertiary  Goes by SN2 mechanism o Reminder- alkyl halides only get reactions at sp3 centers- not sp2 – this holds true for alcohols as well o Make sure to remember to always label the type of carbon (primary, secondary, tertiary 3. Dehydration to Alkenes - Substitution reactions always accompanied by elimination o What favors E over substitution?  Big bulky base  Stable double bond o *Know chapter 7* - Elimination to form double bonds in especially favored when stable double bonds are formed - Alkyl groups stabilize it - When you have alternatives- you will always form the more stable double bond - ** Alcohol with an acid going to get elimination- sometimes get the potential for different products- The most stable double bond is going to be the best yield and more favorable product 4. Oxidation of primary and secondary alcohols - So many oxidizing agents - Only primary and secondary alcohols react - Tertiary alcohols cannot be oxidized to simple carbonyl compounds - Tertiary carbons are NOT oxidized - When you go to oxidize primary alcohols  problem o Take the hydrogen off
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