Amines and lipids Flashcards
(27 cards)
Are aliphatic or aromatic amines more basic?
- Amines are usually basic, but aliphatic (non-aromatic) bases are usually more basic than aromatic amines.
This is because aromatic amines have delocalised e- that can stabilise the NH bond and donate e- density: e- can stabilise across the ring
Thus aliphatic stronger: fewer ways charge can be placed
Friendly reminder: acids give up H+, bases accept them, which would give them a more +ve charge,
Are aliphatic or aromatic amines more basic?
- Amines are usually basic, but aliphatic (non-aromatic) bases are usually more basic than aromatic amines because they can more readily donate e- density (e- density bound less tightly).
This is because aromatic amines have delocalised e- that can stabilise the NH bond and donate e- density: e- can stabilise across the ring so they’re less available to be donated.
Are amides as basic as amines?
Amides are non-basic because the e- are delocalised over 3 atoms.
- N lone pair interacts with carbonyl via resonance
- Electronegative carbonyl oxygen inductively withdraws e- density
What makes a molecule aromatic?
For a molecule to be aromatic it must satisfy huckel’s law of aromaticity….
–> Must be completely conjugated with (4n+2) pi electrons.
Pyrrole vs pyridine?
- Pyrrole: needs N lone pair for aromaticity because 5-membered ring so it can’t be donated.
- Pyridine: doesn’t need N lone pair bc 6 membered ring. Thus good base bc it CAN be donated.
What’s an amine?
Any derivative of ammonia with H atoms substituted for C (can be entirely substituted: just an -N- in a chain like an ether linkage but nitrogen)
What is the e- domain geometry of ammonia?
Trigonal pyramidal with lone pair at apical position.
Why does N have a lone pair?
the OG N has a full s orbital and then all 3 p orbitals are half full. The result is when you excite you still have one full orbital which has no space or need to bond, so you excite s up, fill up a P then hybridise the rest…. Result is 3 spots for H to sigma bond to, and one lone sp pair left also.
- -> Lone pairs are hybridised also.
- -> Note: for double bonds you need an unhybridised singly occcupied P orbital.
Carbon has one less electron (and one less proton) (starting point full s and 2 half full p) so this means after exication you have four half full orbitals to hybridise and hence four possible bonding sites. However if you added an electron to make a lone pair, because it has less protons it would actually be a carboanion.
What’s a 1° amine?
1°: one H substitued
2°: two H subbed
3°: 3 H subbed.
4°: 4H subbed. For this to be possible, has to donate lone pair and become a cation.
What sort of amine is most nucleophilic?
1° and 2° are most nucleophilic because of lone pair.
What’s useful about amine salts?
- Amines are water soluble in the salt form
- Amines more stable bc lone pair tied up + can’t react
- Enables separation of amines from other mixtures of organic compounds.
- Good for pharmacists.
How can you synthesis amines?
- Reduction of amide into a 1° amine
- Reduction of a nitrobenzene
- Reduction of a nitrile
How do amines react?
There are two broad classes of amine reactions:
+ Alkylation:
- SN2 with alkyl halides
+ Acylation: nucleophilic acyl substitution
- With acid chlorides.
What defines a lipid?
A lipid is any molecule that is soluble in organic solvents but not water.
- Based off a physical not chemical property
What are the three major biological roles of lipids?
Lipids are useful for…
- Energy storage
- Chemical messaging
- Membranes
Triglyceride vs fatty acid?
Triglyceride is MADE of fatty acids with glycerol.
Both have
Meaning of saponifiable?
able to become hydrolysed to an acid and an alcohol as a result of treatment with an alkali.
Meaning of saponifiable?
able to become hydrolysed to an acid and an alcohol as a result of treatment with an alkali.
What is a lipid bilayer made of?
A phospholipid bilayer can be made from phosphoglyceride groups.
What’s the structure of a steroid?
Steroids are made of fused 3 cyclohexanes and 1 cyclopentane. AB on lower half and CD on top half (D is pentane). BC and CD rings are trans-fused
Why are fatty acids insoluble?
Fatty acids are usually insoluble because the non-polar tail is larger than the polar head.
Why is it important that unsaturated fatty acids have cis bonds?
Because cis bonds kink the structure leading to lower MPs/BPs while trans bonds form a linear structure that forms a more solid structure.
Why do saturated fatty acids have higher melting points?
Saturated fatty acids have higher melting points because their structure is more ordered so higher dispersion forces and attraction between chains. Cis double bonds kink the structure, making it less ordered and so disrupting dispersion forces.
Thus the MP decreases as the no. of double bonds increases.
Saturated: solids at room temp
Unsaturated: liquids at room temp.
How does MP change for triglycerides with molecular weight and number of double bonds?
MP inc. as MW inc (bc lengthens non-polar tail)
MP dec. as no. C=C inc.
