O Chem 1 Flashcards
Hydrocarbons
Organic compound containing C and H atoms only.
Meth- 1C Eth- 2C Prop- 3C But- 4C Pent- 5C Hex- 6C Hept- 7C -ane, -ene, -yne -> depend on type of bonds present.
Alkane
only single bonds between C atom (saturated hydrocarbons) : CnH(2n+2).
Alkene
contain at least one C=C (carbon to carbon double bond): CnH(2n).
Alkyne
Contain at least one carbon to carbon triple bond: CnH(2n-2).
Aromatic
cyclic molecule with resonance (contains benzene-like molecule).
Ring strain
of cyclic hydrocarbons:
-Sp^3 carbon atoms are tetrahedral therefore prefer to have a bond angle of 109.5.
-In a ring structure, the bond angle between attached carbons is often significantly below 109.5 -> destabilizing.
Degrees of Unsaturation (DoU)
Indicates number of pi bonds and/or rings.
-1 ring: 1 DoU; 1 pi bond= 1 DoU
- Double bond: 1 DoU
- Triple bond: 2 DoU
- Benzene: 4 DoU
- DoU = (2C+2-H)/2
- C: # carbons, # hydrogens and/or halogens
- If nitrogen present, count as one additional C and one additional H.
Carbocation
Molecule with a carbon atom that has a +1 charge (only has 3 bonds to it).
-Doesn’t have full octet; unstable
Carbanion
Molecule with a carbon atom that has a -1 charge (has 3 bonds to it plus a lone pair).
-Has full octet but unstable because -1 FC on atom with low EN
Electron Donating Groups
Atoms/groups of atoms with low EN (alkyl groups).
-EDGs minimize the effect of a + charge
Electron Withdrawing Groups
Atoms/group of atoms with high EN (O, N, F, Br, Cl, etc.).
-EWGs minimize the effect of a - charge.
Stability of carbocations
3 > 2 > 1 > methyl
- More EDGs (alkyl groups) => more stable
- More EWGs (EN atoms) => less stable
- If a carbocation has resonance then the molecule is more stable (the + or - charge is delocalized).
Stability of Carbanions
methyl > 1 > 2 > 3
- More EWGs => more stable
- More EDGs => less stable
- If a carbanion has resonance then the molecule is more stable (the + or - charge is delocalized)
Acidity
Molecule with a more stable to conjugate base => more acidic.
- Increasing EN of the atom that loses the H (and gets a -charge as a conjugate base).
- Increasing resonance of conjugate base (delocalizing the -charge).
- Increasing size/polarity of the atom that has a - charge (HCl > HF)
Basicity
Molecule with a more stable conjugate acid = more basic.
- Opposite trends as acidity (i.e. decreasing EN of atom that gains H; smaller atom that gains the H atom).
- Less resonance of base (CH3CH2NH2 > C6H5NH2).
- Atomic groups that are poor LGs are in general stronger bases.
Nucleophile
Donates a pair of electrons to an electrophile, forming a bond (Lewis base).
- Pi bond or atom with a lone pair.
- Likes and attacks positively charged species (“nucleo” “Phile”).
-Common nucleophiles:
Halides (I-, Br-, etc.); OH-, RO-, NH3, NH2-, CN-
Nucleophilicity increases with…
- Increasing negative charge of atom that acts as nucleophile (NH2- > NH3).
- Increasing size/polarity of atom (I- > Cl-; SH- > OH-).
- Decreasing EN because better at sharing its pair of e-.
- Generally, strong bases are good nucleophiles (Bronsted-Lowry base is a nucleophile that attacks and forms a bond with a hydrogen).
- Decreasing steric hindrance.
Electrophile
Electron deficient species that accepts an electron pair by forming a bond with a nucleophile.
-Lewis acid
-Has + or partial+ and/or an incomplete octet
-Common electropholes:
H+, H3O+, BF3, Partial+C
Leaving group
Better LG= more stable existing on its own (apart from the molecule that it leaves) and better at holding the e- (and the negative charge) that it receives.
-Weak bases (conjugates or strong acids) = good LG
