Chem - Organic chem SL&HL Flashcards
What is Organic Chemistry
Field of chemistry which studies carbon-based compounds
What is a homologous Series
- a series of compounds of the same family, with the same general formula, which differ from each other by a common structural unit.
- homologous series which contain functional group also have similar physical and chemical properties within the series.
Physical properties of homologous series
as length of the chain increases:
- the boiling point increases
- increase in SA
- greater chance of intermolecular bonding
- more energy to break bonds
IUPAC - root names, based off of number of C atoms
1 Cabon: meth-
2 Carbon: eth-
3 Carbon: prop-
4 Carbon: but-
5 Carbon: pent-
6 Carbon: hex-
7 Carbon: hept-
8 Carbon: oct-
IUPAC - identifying the type of bonding in chain or ring
a. all single bonds: -an-
b. one double bond: -en-
c. one triple bond: -yn-
IUPAC - identify functional or alkyl group
Alkane: -e
Hydroxyl: -ol
Amine: amino-
Amide: -amide
Nitrile: -nitrile
Halo: chloro-,bromo-, iodo-
Aldehyde: -al
Ketone: -one
Carboxylic Acid: -oic acid
ether: -oxy-
ester: -oate-
what is the last step of IUPAC naming?
use numbers to give position of groups or bonds along chain, always choosing the lowest number
Primary compounds
C-atoms bonded to functional group is also bonded to ONE other C-atom
Secondary compounds
C-atom bonded to functional group is also bonded to TWO other C-atoms
Tertiary compounds
C-atom bonded to functional group is also bonded to THREE other C-atoms
Alkanes
Hydrocarbons
- contain hydrogen and carbon only
CnH2n+2
- only single bonded
- saturated
- “-ane”
Alkenes
Hydrocarbons
- contain hydrogen and carbon only
CnH2n
- double bond
- unsaturated
- “-ene”
- position of double bond must be specified
-functional group: alkenyl
Alkynes
Hydrocarbons
- contain hydrogen and carbon only
CnH2n-2
- triple bond
- unsaturated
- “-yne”
- position of triple bond must be specified
-functional group: alkynyl
Arenes
Hydrocarbons
- contain hydrogen and carbon only
CnHn
- collective name given to compounds with one or more rings with pi electron that are delocalised throughout the rings
- functional group: phenyl
- Benzene
Halogenoalkanes
CnH2n+1X
- X - halogen
- “chloro-“, “bromo-“, “iodo-“
- “-ane”
- position of the halogen must be specified by numbering the Carbon
- if there is more than on of each halogen - di,tri or tetra must be used
Alcohols
functional group: -OH, hydroxyl
- CnH2n+1OH
- “-ol”
- primary,secondary, tertiary
Ethers
functional group: R – O –R, ether
- CnH2n+2O
- each R-group is given an alkyl name
“-ane”
Carbonyls
functional group: C=O
- CnH2nO
- subfamilies: aldehyde and ketone
Aldehydes
- when carbonyl group is a tthe end of the chain
functional group: -RCHO - “-al”
- will always be on number 1 carbon
Ketones
-minimum of 3 carbons
functional group: RCOR
-“-one”
- # for carbon must be used
aldehydes vs ketones
show similar chemical reactions - similar functional groups arrangments
differences in chemistry are due to the involvements of the H in aldehyde or nature of R group
differences in electronegativity between C=O menas its polar
- dipole attraction between molecules
- higher boiling point
-solubiliyt in water
Carboxylic acid
functional group: carboxyl, -COOH
-CnH2n+1COOH, RCOOH
- “-oic acid”
Esters
functional group: carboxylate, -COOR
- RCOOR
- “-oate”
alkyl + alkanoate
e.g. methyl ethanoate
carboxylic acids vs esters
contain similarities in chemical and physical properties
- H-bonds are present between carbpxylic acid molecules, and not between esters.
- this affects melting, boiling ang solubility
- carboxylic acids: smaller chain are soluble in water and have higher melting points
- esters: insoluble in water and have lower boiling points than carboxylic acids
Amines
functional group: -NH2
-CnH2n+2NH2, RNH2
“amino+alkane”
Amides
functional group: carboxamide, -CONH2
combination of amino and carbonyl groups
- CnH2n+1CONH2, RCNH2
- “-amide”
Nitriles
functional group: nitrile, -CN
-CnH2n+1CN, RCN
-“-nitrile”
what symbolises a bond going away from you in a stereochemical drawing
what symbolises a bond going towards you in a stereochemical drawing
Why are alkanes unreactive?
Strength of C-H bonds
- alkanes consist of C and H bonded by single bonds
- without heat, it’s hard to break these strong C-C and C-H covalent bonds
Lack of polarity
- electronegativites of C and H are almost similar
- electrons shared equally
- alkanes don’t react with polat reagents, as they have no nucleophilic or electrophilic areas
alkanes only react in combustion reactions and undergo substitutions by halogens
Complete combustion of Alkane
when alkanes are burnt in XS O2, complete combustion takes plane, and all C and H will oxidise to CO2 and H2O
Incomplete combustion of Alkane
when alkanes are burnt in limited supply of O2, incomplete combustion will take place and not all C-atoms fully oxidise.
Alkane + Oxygen –> CO + H2O
CO is a toxic gas, will bind to haemoglobin in blood which can then no longer bind to O2
CO is odorless, and found in car engines where O2
Free radical sustitution
Steps 1-3
alkanes - halogenations
u.v. light (sunlight) is needed
a hydrigen atom gets substitutes by a halogen
1. inititation step
- Halogen bond is broken by UV energy to form two radicals
- produces two radical in a homolytic fission reaction
- propegation step
- progression of the substitution reaction in a chain type reaction
- free radicals are very reactive, and will attack unreactive alkanes
- a C-H bond breaks homolytically ( each atom gets an e- from covalent bond)
- an alkyl free radical is produced
- which can attack another halogen to form halogenoalkane and regenerate the halogen bond
- this reaction is not verys uitable for preparing specific halogenoalkanes as a mixture of substitution products are formed
- if there is enough halogens present, all the hydrigens in the alkane will eventually substituted - termination step
- when the chain reaction terminates due to two free radicals reacting together and forming a single unreactive molecule
- multiple products possible
reactivity of alkenes
C=C bonds gives alkanes a number of chemical properties not seen in alkanes
- alkenes contain pi-bonds, it is possible to break the weaker pi-bonds and form stronger σ bonds with other species withoit forcing any atom on the molecule to break off
- alkenes are able to undergo substitutions
- can undergo addition
- unsaturated
- addition reactions are faster than substitution reaction as only weak pi-bonds are broken rather than σ bonds.
What is the test for unsaturated alkenes?
Br2 - yellow, orange solution, “bromine water”
- unknown molecule/compound is shaken with bromine water
- if compound is unsaturated - addition will take place and color is lost
Alkenes Halogenation
electrophilic addition - more detail in other flashcard
- C=C doubel bond is broken, and a new single bond is formed from each of the two C atoms
- occurs at room temperature
- halogens can be used to test if molecule is unsaturated
electrophile
‘electron seeker’
has a positive charge
nucleophile
‘wants to give away electrons’
negative charge
Alkenes Hydration
- when alkenes are reacted in steam at 300°C, pressure at 60 atm, and sulfuric acid/phosphoric acid catalyst, water is added to the double bond
- alkene —> alcohol
- reaction processes via an intermediate in which H+ and H2SO4- ions are added. across double bond
- the intermediate is quickly hydrolyseed by water, reforming H2SO4
Addition Polymers
- most important addition reaction of alkenes
- is the reaction in which many monomers containing at least one C=C double bond form long chain of polymers as the only product
- the pi-bond in each C=C breaks and monomers link together to form C-C
- polymer - long chain that is made up of repeating units
- small, reactive molecules that react together to from the polymer are called monomers
how do you deduce repeating units in polymers
- repeated unit is the smallest group of atoms that when connected one after the other make up the polymer chain
- square brackets
- in poly(alkenes) and substituted poly(alkenes) made up of one type of monomer the repeating unit is the same as the monomer except that the C=C double bond is changed to C-C
complete combustion of alcohols
- Alcohol + Oxygen —> CO2 and H2O
- lower alcohols burn with an almost invisible flame and make good fuels
- ethanol can be produced sustainably as a fuel by the fermentation of sugars
- ethanol has a lower energy density is lower than gasoline, therfore blending ethanol and gasoline increases energy denisty, makes it safer in case of fires as the flames can be seen
Oxidation of Primary Alcohol
oxidise to form aldehydes and then carboxylix acids
oxidising agents: K2Cr2O7 or KMnO4
Potassium dichromate: K2Cr2O7
- orange
- in a solution of dilute acid
- orange Cr2O7 (2-) ions–> greenCr (3+) ions
Potassium Manganate: KMnO4
- purple
- in a solution of dilute acid
- purple MnO4(-) ions –> colorless Mn(2+)
In XS Oxidising agents, if the aldehyde produced isn’t distilled off, it will further oxidise to carboxylic acids, however this reaction takes some time to complete and requires heating.
Tests for alcohols:
- oxidation using acidified dichromatic provides basis for the test for alcohols as it shows color change
- orange –> green
- does not work for tertiary alcohols
Oxidation for secondary alcohols
- oxidise to ketones
- under sustained heating
Oxidation for tertiary alcohols
- DO NOT undergo oxidation
- there are only C-C bonds on functional group carbon in tertiary alcohols
- no H that can break off to form water
distillation vs heating under reflux
Alcohols esterifications
ester: -COOR, sweet, fruity smell
- formed via condensation reactions between Crboxylic acids and Alcohols, with concentrated H2SO4 as catalyst
esterification : NUCLEOPHILLIC SUBSTITUTION
naming ester: first part of alcohol, second part: carboxylic acid
Reactions of Halogenoalkanes
- much more reactive than alkanes due to presence of electronegative halogens
- X-C bond is polat, C - carries partial + charge, X - carries partial - charge
Nucleophilic substitutions with NaOH - halogenoalkane + aq alkali –> alcohol
- OH- behaves as nucleophile by donating a pair of e- to - C-atom bonded to halogen
- reaction is slow at room temp.
- high yield when heated under reflux
Reactions of Benzene
Arenes are very stable compounds due to delocalisation of pi e- in the ring,
- e- density is spread ou over the molecules
during substitution: ring is maintained
during addition: aromatic stabilisation is disturbed so it’s not favored
electrophilic substitution with benzene
with Cl2 or Br2 in the presence of anahydrous AlCl3 or AlBr2 catalysts to form halogenoarene
- cl/br acts as electrophile and replaces H atom in benzene
- catalyst necessart due to stability of benzene structure
- alkylarenes such as methylbenzene undergo halogenation on the 2 or 4 position, which is due to e- donating alkyl group which activates these positions.
- ∴the halogenation of alkylarenes results in the formation of 2 products
- in xs halogen, it joins at the 2 or 4 or 6 positions
-
Nitration of Benzene
- substitution
- a nitro (NO2) group replaces H atom on arene
- benzene is reacted with mixture of conc. nitric acid and conc. sulfuric acid at 25-60℃
- occurs at 2 and 4 positions
Nucleophilic Substitutions (HL)
- organic reaction in which nucleophile attacks a carbonyl C-atom with partial + charge.
- atom attaches to carbonyl has a -charge and is replaces by nucleophile
- involves halogenoalkanes, the halogen is replaced by nucleophile
- the OH-, is stronger nucleophile than H2O, bc it has a full - charge
- strength of nucleophile depends on it’s abolity to make its e- pairs available for reactions
in general: - charged ions > neutral atom
conjugate base > conjugate acid
OH->H2O
SN1 (w Arrows)
- tertiary halogenoalkanes - C attached to halogen i salso bonded to 3 alkyl groups
1 stands for the rate of reaction
SN1 is 2 steps
First step: - C-X bond breaks heterotically and the halogen leaves the halogenoalkane as an X- ion
- slow, rate determining step
- only depends on the conc. of halogenoalkane
- rate= k(halogenoalkane)
- forms a tertiary carbocation ( tertiary C with + charge)
Second step: - the tertiary carbocation is attacked by nucleophile
Heterolytic fission
forms anions and cations and used double headed arrows to show movement of both e- from covalent bonds
Homolytic fission
forms free radicals and uses single headed arrows, “fish hooks”, to show the moevement of a single e- as a covalent bond breaks
SN2
- Primary halogenoalkanes, the C attached to the halogen is bonded to one alkyl group
2 stands for rate of reaction
SN2 is one step reaction - nucleophile donates a pair of e- to the g+ C atom of the halogenoalkane to form a new bond
- rate determining step depends on the conc. halogenoalkane and nucleophile
- rate=k(halogenoalkane)(nucleophile)
- at the same time, the C-X bond breaks and the halogen takes both e- in the bond
- the halogen leaves the halogeno alkane as X- ion
- nucleophile can only attack from oppisite direction of C-X bond
- as C-Nucleophile bond forms, C-Br bond breaks causing X atom to leave as an ion.
What factors affect SN1 and SN2
- nature of nucleophile
- halogen involved
- the structure (class) of halogenoalkane
- protic and aprotic solvents
How does the nature of the nucleophile affect SN1&2
most effective nucleophiles are neutral or - charged species, that have lone pair of e- avaliable to donate to the g+ C in halogenoalkane
- greater the e- density on the nucleophile ion or molecule – the stronger the nucleophile
- when nucleophiles have some charge, the electronegativty of the atom carrying the lone pair becomes the deciding factor
- less electronegative the atom = stronger nucleophile
- less electronegative atom has a weaker grip on lone pairs e-
How does the halogen involved affect SN1&2
- the halogenoalkane have different rates of substitution reactions
- C-I bond is the weakest and easiest to break
- C-F bond is the strongest and hardest to break
- floroalkanes –> chloroalkanes –> bromoalkanes –> iodoalkanes
- least reactive –> most reactive
how does the structure of the halogenoalkane affect SN1&2
- tertiary halogenoalkane –> SN1, forms stable tertiary cabocations
- -secondary –> mixture of SN1 and 2, forming less stable primary carbocations
- this has to do with + inductive effect of alkyl group attached to C-X
- tertiary carbocation - 3 alkyl groups
- primary - 1 alkyl group, less stable
How do protic and aprotic solvents affect SN1&2
Protic solvents
- contain a H atom bonded to electronegative N or O
- capable of hydrogen bonding
Aprotic solvents
- contain H atom but not bonded to eelctronegative atom
- cannot participate in H-bonding
SN1 - best conducted using protic, polar solvents
SN2 - best conducted using aprotic, non-polar solvents
Electrophilic Addition
addition of an electrophile (lewis acid) to an alkene double bond, C=C
- C=C , is an area of high electron density which makes it susceptible to attack by electrophiles
- C=C bond breaks forming a C-C bond and 2 new bonds
Electrophiles
- H2(g)–> alkane
- H2O(g) –> alcohol
- HX, hydrogen halides –> halogenoalkane
- X2, halogen –> dihalogenoalkane
Electrophilic addition of HX
