3.2 Synthesis Flashcards
types of bond fission
- homolytic
- heterolytic
- homolytic
- heterolytic
types of bond fission
bond fission
bond breaking
homolytic fission
- results in the formation of two neutral radicals
- occurs when each atom retains one electron from the sigma covalent bond and the bond
breaks evenly - normally occurs when non-polar covalent bonds are broken
- tend to result in the formation of very complex mixtures of products, making them unsuitable for organic synthesis
- results in the formation of two neutral radicals
- occurs when each atom retains one electron from the sigma covalent bond and the bond
breaks evenly - normally occurs when non-polar covalent bonds are broken
- usually to result in the formation of very complex mixtures of products, making them unsuitable for organic synthesis
homolytic fission
heterolytic fission
- results in the formation of two oppositely charged ions
- occurs when one atom retains both electrons from the σ covalent bond and the bond breaks unevenly
- normally occurs when polar covalent bonds are broken
- usually result in far fewer products than reactions involving homolytic fission, and so are better suited for organic synthesis
- results in the formation of two oppositely charged ions
- occurs when one atom retains both electrons from the σ covalent bond and the bond breaks unevenly
- normally occurs when polar covalent bonds are broken
- usually result in far fewer products than reactions involving homolytic fission, and so are better suited for organic synthesis
heterolytic fission
what are attacking groups classified as in reactions involving heterolytic bond fission
- nucleophiles
- electrophiles
when are groups classified as nucleophiles or electrophiles
if they are an attacking group in heterolytic bond fission
nucleophile
- negatively charged ions or neutral molecules that are electron rich, such as
Cl−, Br−, OH−, CN− , NH3 and H2O - attracted towards atoms bearing a partial (δ+) or full positive charge
- capable of donating an electron pair to form a new covalent bond
- negatively charged ions or neutral molecules that are electron rich, such as
Cl−, Br−, OH−, CN− , NH3 and H2O - attracted towards atoms bearing a partial (δ+) or full positive charge
- capable of donating an electron pair to form a new covalent bond
nucleophiles
electrophile
- positively charged ions or neutral molecules that are electron deficient, such as H+,NO2+ and SO3
- attracted towards atoms bearing a partial (δ−) or full negative charge
- capable of accepting an electron pair to form a new covalent bond
- positively charged ions or neutral molecules that are electron deficient, such as H+,NO2+ and SO3
- attracted towards atoms bearing a partial (δ−) or full negative charge
- capable of accepting an electron pair to form a new covalent bond
electrophile
haloalkane
- aka alkyl halides
- substituted alkanes in which one or more of the H atoms is replaced with a halogen atom
- aka alkyl halides
- substituted alkanes in which one or more of the H atoms is replaced with a halogen atom
haloalkane
monohaloalkane
- contain only one halogen atom
- can be classified as primary, secondary or tertiary according to the number of alkyl groups attached to the carbon atom containing the halogen atom
- take part in elimination reactions to form alkenes using a strong base, such as potassium or sodium hydroxide in ethanol
- take part in nucleophilic substitution reactions with:
— aqueous alkalis to form alcohols
— alcoholic alkoxides to form ethers
— ethanolic cyanide to form nitriles (chain length increased by one carbon atom) that can be hydrolysed to carboxylic acids - can take part in nucleophilic substitution by one of two mechanisms: sn1 or sn2
mechanisms for monoalkanes in nucleophilic substitution
- sn1: nucleophilic substitution reaction with one species in the rate determining step and occurs in a minimum of two steps via a trigonal planar carbocation intermediate
- sn2: nucleophilic substitution reaction with two species in the rate determining step and occurs in a single step via a single five-centred, trigonal bipyramidal transition state
- sn1: nucleophilic substitution reaction with one species in the rate determining step and occurs in a minimum of two steps via a trigonal planar carbocation intermediate
- sn2: nucleophilic substitution reaction with two species in the rate determining step and occurs in a single step via a single five-centred, trigonal bipyramidal transition state
mechanisms for monoalkanes in nucleophilic substitution
alcohol
substituted alkanes in which one or more of the hydrogen atoms is replaced with a hydroxyl group, OH-
substituted alkanes in which one or more of the hydrogen atoms is replaced with a hydroxyl group, OH-
alcohol
what can alcohols be prepared from
- haloalkanes by substitution
- alkenes by acid-catalysed hydration (addition)
- aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride
what can be prepared from the following
- haloalkanes by substitution
- alkenes by acid-catalysed hydration (addition)
- aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride
alcohols
reactions of alcohols
- dehydration to form alkenes using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid
- oxidation of primary alcohols to form aldehydes and then carboxylic acids and secondary alcohols to form ketones, using acidified permanganate, acidified dichromate or hot copper(II) oxide
- formation of alcoholic alkoxides by reaction with some reactive metals such as potassium or sodium, which can then be reacted with monohaloalkanes to form ethers
- formation of esters by reaction with carboxylic acids using concentrated sulfuric acid or concentrated phosphoric acid as a catalyst
- formation of esters by reaction with acid chlorides ( R-COCl) — this gives a faster reaction than reaction with carboxylic acids, and no catalyst is needed
- dehydration to form alkenes using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid
- oxidation of primary alcohols to form aldehydes and then carboxylic acids and secondary alcohols to form ketones, using acidified permanganate, acidified dichromate or hot copper(II) oxide
- formation of alcoholic alkoxides by reaction with some reactive metals such as potassium or sodium, which can then be reacted with monohaloalkanes to form ethers
- formation of esters by reaction with carboxylic acids using concentrated sulfuric acid or concentrated phosphoric acid as a catalyst
- formation of esters by reaction with acid chlorides ( R-COCl) — this gives a faster reaction than reaction with carboxylic acids, and no catalyst is needed
reactions of alcohols