Flashcards in Organic Nitrogen Test Deck (40):
Boiling point trend in amines
• Boiling points increase with molecular mass. • Amines have higher boiling points than corresponding alkanes because of intermolecular hydrogen bonding.
Solubility of amines
• Soluble in organic solvents. • Lower mass compounds are soluble in water due to hydrogen bonding with the solvent. • Solubility decreases as molecules get heavier.
Why are amines bases?
The lone pair on nitrogen makes amines basic. RNH2 + H+—> RNH3+
Strength of bases in amines
• depends on the availability of the lone pair and thus its ability to pick up protons• the greater the electron density on the N, the better its ability to pick up protons• this is affected by the groups attached to the nitrogen.
What decreases basicity of amines?
Electron withdrawing substituents (e.g. benzene rings) decrease basicity as the electron density on N is lowered.
What increases basicity of amines?
Electron releasing substituents (e.g. CH3 groups) increase basicity as the electron density is increased
The strength of a weak base is depicted by what?
the strength of a weak base is depicted by its Kb or pKb value• the larger the Kb value the stronger the base• the smaller the pKb value the stronger the base.• the pKa value can also be used - ( pKa + pKb = 14 )• the smaller the pKb, the larger the pKa.
Amines which dissolve in water produce...
Weak alkaline solutionsCH3NH2(g) + H2O(l) --> CH3NH3(aq) + OH+
Amines react with acids to produce...
SaltsC6H5NH2(l) + HCl(aq) —> C6H5NH3+ClAddition of aqueous sodium hydroxide liberates the free base from its saltC6H5NH3+Cl ̄(aq) + NaOH(aq) —> C6H5NH2(l) + NaCl(aq) + H2O(l)
Due to their lone pair, amines react as nucleophiles with...
• haloalkanes forming substituted amines- nucleophilic substitution• acyl chlorides forming N-substituted amides- addition-elimination
Amines can be prepared from haloalkanes
Reagent Excess, alcoholic ammoniaConditions Reflux in excess, alcoholic solution under pressureProduct Amine (or its salt due to a reaction with the acid produced)Nucleophile Ammonia (NH3)Equation C2H5Br + NH3 (aq / alc) ——> C2H5NH2 + HBr
Why excess ammonia with amines prepared from haloalkanes?
The amine produced is also a nucleophile and can attack another molecule of haloalkane to produce a secondary. This in turn can react further producing a tertiary amine and, eventually an ionic quarternary amine. By using excess ammonia, you ensure that all the haloalkane molecules react with ammonia rather than the newly produced haloalkane.
Amino acids contain what two functional groups.
• amine NH2• carboxyl COOH
Amino acids can exist as optical isomers if they have different R1 and R2 groups
• optical isomers exist when a molecule contains an asymmetric carbon atom• asymmetric carbon atoms have four different atoms or groups attached• two isomers are formed• one rotates plane polarised light to the left, one rotates it to the right• no optical isomerism with glycine - two H’s are attached to the C atom
What is a zwitterion?
• a zwitterion is a dipolar ion• it has a plus and a minus charge in its structure• a proton from the COOH group moves to NH2• amino acids exist as zwitterions at a certain pH• the pH value is called the isoelectric point• produces increased inter-molecular forces• melting and boiling points are higher
Acidic/basic properties of amino acids.
• amino acids possess acidic and basic properties due to their functional groups• they will form salts when treated with acids or alkalis.
How are peptides formed?
α-amino acids can join up together to form peptides via an amide or peptide link• 2 amino acids joined dipeptide• 3 amino acids joined tripeptide• many amino acids joined polypeptide
Peptides can be broken down into their constituent amino acids by...
Hydrolysis• attack takes place at the slightly positive C of the C=O• the C-N bond next to the C=O is broken• hydrolysis with just water is not feasible• hydrolysis in alkaline/acid conditions is quicker• hydrolysis in acid/alkaline conditions (e.g. NaOH) will produce salts
What are proteins?
• polypeptides with high molecular masses• chains can be lined up with each other• the C=O and N-H bonds are polar due to a difference in electronegativity• hydrogen bonding exists between chains
Structure of amides
Based on a carboxylic acid (remove OH, add NH2)
Appearance of amides
White crystalline solid
Nomenclature of amides
Named from the corresponding acid (remove oic acid... add amide)
Preparation of amides
Acyl chloride + ammonia (or amines for 2° amides)e.g. CH3COCl(l) + NH3(aq) —> CH3CONH2(s) + HCl(g)
Hydrolysis of amides
general reaction: CH3CONH2 + H2O —> CH3COOH + NH3acidic soln.: CH3CONH2 + H2O + HCl —> CH3COOH + NH4Clalkaline soln.: CH3CONH2 + NaOH —> CH3COONa + NH3
Identification of amides
Warming with dilute sodium hydroxide solution and testing for the evolution of ammonia using moist red litmus paper is used as a simple test for amides.
Reduction of amides
Reduced to primary amines:CH3CONH2 + 4[H] ——> CH3CH2NH2 + H2O
What is the simplest amine?
Aromatic amines have...
The N joined directly to the benzene ring.
Quaternary ammonium salts contain...
Quaternary ammonium ions and are related to amines, but they are not amines and do possess a lone pair of electrons on the N.
Quaternary ammonium salts with some long chain alkyl groups are used as...
Reduction of nitrile compounds to form amines
This is the commonest way and is usually done in twosteps:a) producing a nitrile compound from a haloalkaneb) then reducing the nitrile compound
What is the stronger base out of methylamine and diethylamine?
Diethylamine- diethylamine is 2y amine whereas methylamine is 1y amine; ∴ more electron density pushed onto N lone pair in diethylamine ∴ diethylamine better at accepting H+
What is the stronger base out of propylamine and phenylamine?
Propylamine- propylamine is 1y amine whereas phenylamine is aromatic amine; ∴ more electron density pushed onto N lone pair in propylamine (in phenylamine electron density is delocalised into the ring away from the N) ∴ propylamine better at accepting H+
What is the stronger base out of ammonia and phenylmethylamine?
Phenylmethylamine- phenylmethylamine is 1y∴ more electron density pushed onto N lone pair in phenylmethylamine ∴ phenylmethylaminebetter at accepting H+ amine compared to ammonia
What is the stronger base out of ammonia and cyclohexylamine?
Cyclohexylamine- cyclohexylamine is 1 amine compared to ammonia ∴ more electron density pushed onto N lone pair in cyclohexylamine ∴ cyclohexylamine better at accepting H+
In general, the order of base strength is:
tertiary > secondary > primary > NH3 > aromatic
3y,2y,1y amines compared to ammonia
• Compared to ammonia, the more alkyl groups that are substituted onto the N atom in place of H atoms, the more electron density is pushed onto the N atom (as the inductive effect of alkyl groups is greater than that of H atoms -so alkyl groups push electron density towards the N atom better than H atoms). • So the more alkyl groups, the higher the electron density of the lone pair on the N, so the stronger the base.
Aromatic amines compared to ammonia
• The lone pair on this N is partially delocalised into the benzene ring, leading to a reduction in the electron density on the N atom, so weaker base strength.
acid/base reactions of amino acids...with acids
with acidsreagents: HClconditions: room temperatureequation: R-CH(NH2)-COOH + HCl ---> R-CH(NH3+Cl-)-COOH