O Chem Flashcards
Define: hydrocarbon
Molecule that consists entirely of carbon and hydrogen
Define: structural isomers
Same molecular formula, but different connectivity of atoms
Geometric isomers
Double bonded alkene, atoms are connected in same order, but differ in the configuration of atoms around double bond (cis and trans isomers)
What state are fats with cis conformations at room temp, and why?
Liquid, cis conformation prevents tight packing
Define: enantiomer
Same chemical structure but differ in their three-dimensional placement of atoms (non-superimposable mirror images), chiral molecules only
Which isomer (D or L) of amino acids are found in nature/humans?
L
Which isomer (D/L) of sugars are found in nature?
D
What is a carboxylic acid group, and is it acidic or basic?
R-COOH, once ionized, it releases H+ into the solution, making it to be considered acidic
What is an amino group, and is it considered acidic or basic?
R-NH2, it accepts H+ to form NH3+…since it removes H+ from the system, it is considered basic
Are hydrogen phosphate groups considered acidic or basic?
Acidic, since they release H+ into the solution
Which has a higher BP and why? Pentane or hexane?
Hexane, longer chain, more molecular weight, more LDF attraction between chains
Which has a higher BP and why? Pentane or neopentane?
Pentane, neopentane is branched, which decreases its surface area, decreasing ability for LDF
Which has a higher BP and why? Hexane or hexanone?
Hexanone, since it has a carboxyl group, it has dipole-dipole interactions as well as LDF, increasing BP
Which has a higher BP and why? Hexanone or hexanol?
Hexanol, it has an OH group, allowing for hydrogen bonding
Which has a reaction intermediate: SN1 or SN2?
SN1 (two steps)
Which is considered bimolecular: SN1 or SN2?
SN2
Which has a reaction intermediate: E1 or E2?
E1
Which is considered unimolecular: E1 or E2?
E1
Which is a more stable carbocation? Allyl or benzyl?
Benzyl
Which has more cationic stability: allyl or tertiary?
Allyl (because of resonance)
If the alkyl chain is a methyl group, which will occur (SN1/2 or E1/2)?
Only SN2
Not SN1 or E1 because unstable carbocation
Not E2 because no Beta-hydrogen
If the alkyl chain is a primary carbon, which will occur (SN1/2 or E1/2)?
SN2 more than E2, but both possible
Not SN1 or E1 because unstable carbocation
If the alkyl chain is a secondary carbon, which will occur (SN1/2 or E1/2)?
SN1 or E1 if a weak nucleophile or base, respectively
SN2 or E2 if strong nucleophile or base
Which do SN1/2 reactions prefer: polar protic or aprotic solutions?
SN1 prefer polar aprotic
SN2 polar protic
Which do E1/2 reactions prefer: polar protic or aprotic solutions?
E1 polar aprotic
E2 Polar protic
If the solution is polar protic, which will be preferred: E2 or SN2?
Either
If the alkyl chain is a tertiary carbon, which will occur (SN1/2 or E1/2)?
SN1 or E1 if weak Nucleophile/base
E2 if strong base
Not SN2 because of steric hindrance
Is a negatively charged molecule a good or bad nucleophile?
Good/stronger
Name some weaker nucleophiles
Neutral: R-OH, H2O, NH3, CH3OH
List leaving groups in order from best to worst:
I-, F-, Cl-, Br-
I-, Br-, Cl-, F-
List leaving groups in order from best to worst:
H2O, OR-, OH-, NH2-, CH3COO-
H2O, CH3COO-, OH-, OR-, NH2-
What makes a good leaving group?
Larger size, ability to support/spread out e- cloud
Does polar protic allow or not allow H bonding?
Allow
List some polar protic solvents
H2O, CH3OH, NH3
List some polar aprotic solvents
DMSO, DMF, Acetone, Acetonitrile
What are the 3 steps for a free radical reaction?
Initiation, propagation, termination
Define: nucleophilicity
Ability for atom/molecule to give away e- and bond (has extra e- to give away)
In a polar aprotic solvent, is I- or F- better nucleophile?
F-
In polar protic solvent, is I- or F- better nucleophile?
I-, doesn’t H-bond like F- would
Is nucleophilicity a kinetic or thermodynamic step?
Kinetic-how good/fast something is at reacting
Is basicity a kinetic or thermodynamic concept?
Thermodynamic, how stable reactants or products are
List these in order of strongest to weakest basicity: OH-, Br-, I-, Cl-, F-
OH- (best), F-, Cl-, Br-, I-
Define: Zeitsev’s rule
In an elimination reaction, the β C more likely to lose H is one with fewer H attached
Electrophiles will have a positive or negative partial/full charge?
Positive
Nucleophiles will have a positive or negative partial/full charge?
Negative
Define: solvolysis reaction
The solvent acts as the nucleophile in an SN reaction
Define: carbocation rearrangement
A tertiary carbocation is more stable than a secondary or primary, so the molecule can move an H or a methyl group to change from a primary or secondary to tertiary carbocation
Does a polar protic solvent favor SN1 or SN2?
SN1, the partially negative portion of the electronegative molecule can stabilize the carbocation, and partial positive portion can stabilize anion leaving group
Does polar aprotic solvent favor SN1 or SN2?
SN2, need a strong nucleophile which would be stabilized in a polar protic solvent
Does a primary substrate favor SN1 or SN2?
SN2, requires decreased steric hindrance
Does a secondary substrate favor SN1 or SN2?
SN2 if it is a strong nucleophile and polar aprotic
SN1 if it is a weak nucleophile and polar protic
Does a tertiary substrate favor SN1 or SN2?
SN1, carbocation stabilization
Describe an SN1 mechanism
- Potential H+ transfer, creating good leaving group
- Loss of a leaving group, carbocation intermediate formed
- Potential carbocation rearrangement
- Nucleophile (solvent) attacks electrophile center of carbocation
- Nucleophile potentially deprotonated
Does an SN1 reaction change stereochemistry?
No, creates racemic mixture