Organic Chemistry Flashcards
Why does O acquire a positive charge when bonded to three atoms? Initially bonded to two atoms
lone pair of electrons on O is accepted by the third atom, and now O has become more electron poor, acquiring a positive charge.
What do you call the intermediate molecules with a singular electron in free radical substitution?
Like, Nsub has carbocation intermediates, what is the equivalence of that in FRS?
Radical intermediate
(CC) explain why alkenes undergo electrophilic addition while carbonyl compounds undergo Nucleophilic addition
The pi electrons in the non polar C=C double bond in alkenes serve as an electron rich source which attracts nucleophiles or induces dipoles in approaching molecules to form electrophiles for reaction
In contrast, the C=O bond in carbonyl compounds is polar where the carbonyl carbon is bonded to the highly electronegative O atom, and is thus electron deficient, bearing a partial positive charge, attracting nucleophiles for reaction
Explain why a racemic mixture is formed if the product of Nucleophilic addition has a chiral carbon
The nucleophile attacks the trigonal planar molecule from the top and bottom of the plane with equal probability —> forming equal proportions of each enantiomer, obtaining a racemic mixture (which is optically inactive)
Write out the chemical equation for reaction of 2,4,DNPH with aldehyde and ketone. What type of reaction is this, and where is the H2O lost obtained from? What does the final molecule look like?
H2 obtained from NH2 in hydrazine part of 2,4DNPH
O obtained from C=O.
Final molecule has a C=N bond
How to prep tollen’s reagent? Describe steps in your own words (don’t need to be exact)
Add 1 drop of NaOH to silver nitrate solution, which forms a brown ppt Ag2O. Add NH3 till ppt JUST dissolves —> [Ag(NH3)2]+ exists in the solution.
What type of reaction is tollen’s reagent?
What is the product formed, and what is the coefficient of OH- in the chemical equation? (For aldehydes)
Oxidation
Product formed: RCOO-, coefficient of OH- is 3
What else other than aldehydes can react with tollen’s reagent, producing silver mirror? (Hint, carboxylic)
Methanoic acid! Coefficient of OH- is 2 though
How to make fehling’s solution and what reaction does it undergo with aliphatic aldehydes?
Blue copper sulfate soln with potassium sodium tartrate in sodium hydroxide solution
Oxidation!
State the RNC for iodoform test as well as the observations
Pale yellow ppt of CHI3 formed, brown aqueous iodine decolorises
Why is LiAlH4 a stronger reducing agent than NaBH4?? (Hint: consider the reducing action of the two.. what ions are released/produced?)
Reduction occurs via the production of H- (hydride) ions by LiAlH4 and NaBH4. LiAlH4 is a stronger RA as it produces H- more readily.
Reason: Al is less electronegative than B. The shared pair of electrons in the Al-H bond lie closer to H than in the B-H bond, thus hydride (H-) ions are produced more readily.
What is hydrolysis (in your own words)?
Breakdown of a compound due to reaction with water. Water MUST be one of the reactants!
Note, salt dissolving to form aqueous ions is NOT hydrolysis
[alkanes] Explain why some cyclic molecules like cyclopropane, cyclobutane are unstable
Unstable due to ring strain. Ring strain arises as the atoms are forced to be in a bond angle of 60 degrees or 90 degrees although sp3 hybridised carbons should ideally have a bond angle of 109.5 to minimise repulsion
[memorise] explain two reasons why aldehydes are more reactive than ketones towards nucleophilic addition
Electrophilic: ED alkyl group in ketone reduces the SIZE of the partial positive charge on carbonyl carbon .
Steric: alkyl group in ketone provides steric hindrance which discourages approach of CN- nucleophile
Explain why amides are neutral
Lone pair of electrons on nitrogen can delocalise into the adjacent C=O group and is unavailable for donation
