chem1aa3 organic chem

Nucleophile

Nucleus loving electron donor Lewis base

Électrophile

Electron loving, electron acceptor Lewis acid

DO E isomers of aliénés have higher melting points than Z-isomers.

YES

Electron flow and curved arrows

Curved arrows used to show how electrons move in bond forming and breaking processes

Rules:

1. Represents movement of pair of electrons

2. Start from source of electron density to source of electron deficiency (-ve to positive)

3. When forming a bond, arrow starts from source of electrons and moves towards an atom

4. When breaking a bond arrow starts from the center of a bond and moves towards atom accepting electrons

Organic reactions key concepts

• nucleophile provides a source of electron dentistry often contains a lone pair of electrons or electron density in a pi bond

• Electrophole has a lack of electron density, often a carbon atom bonded to an electronegative atom. Called a leaving group

• Curved arrows are drawn with the end of the arrow at the nucleophile and head pointing at the électrophone

When methyl or primary alkyl haloes are used

Rate law is kobsAB

methyl alkyl halodes have a large k than primary alkyl halides

Nucleophile is involved in rds

When tertiary alkyl halides are used

Rate law is jobs=A nucleophile is not involved in rds

Secondary alkyl halides are used

Condition dependant experience both rate laws

Nucleophoillic substitution mechanisms

• Addtive

• Concerted

• Dissociative

Additive

from bond then break bond a molecule adds across a multiple bond of another molecule

Concerted draw energy profile diagram

Bonds breaks and form simultaneously

• activation energy increases as electron density around central carbon decreases

• Rate=k(alkyl halide)(nucleophile)

• 2nd order overall

• 1 step mechanism

• Sn2

nucleophillic substitution alcohols, ethers, esters

• hydroxides, alkoxudes, and carboxylates can be used as nucleophiles to make alcohols, ethers, esters, respectively

  • Rate is k(alkyl halides)(nucleophile)

• Water or alcohol can be used as nucleophile and solvent to generate alcohol or ether w a tertiary alkyl halides via sn1

Sn1 vs Sn2

• mechanism depends on many factors

• 1 degree electrophile = sn2, less stable carbocation intermediate, less steric hindrance to nucleophile sttack

• 2 degree electrophole hard to predict generally stronger nucleophiles ones favour sn2

• Third defree electrophile is sn1, since more stable carbocation intermediate, more steric hindrance to nucleophillic sttack

Dissociative and draw energy diagram

Breaks bond then form bond

• activation energy decreases as electron density around central carbon increases

• Rate is k(alkyl halide)

• 1sr order

• 2 step

• Sn1

Hydrohalogenation of alkenes

• When HX adds to the double bond of an alkene

• The h atom adds to the carbon with the smallest number of alkyl groups

• The X atom adds to the carbon atom with the largest number of alkyl groups

• Called markovnikovs rule

Roles in addition reaction

Step 1: alkene is nucleophile and HBr is the electrophile

Step 2: bromide = nucleophile carbocation intermediate = electrophile

Relative stability of carbocations

Stability increases with number of alkyl substituents

Hydration of alkenes

• Alkene plus water turns into alcohol

• Forward reaction favoured in dilute h2s04 (10%)

• Its conjugate base won’t add to cation and Hcl would lead to mixture of hydration and addition products

Hydrogénation (réduction) of alkenes

• alkene plus h2 and catalyst

• Catalyst usually grp 10 metal (Pd, Pt, Ni)

• SYN addition (h atoms add to same face if alkene)

Hydrogénation (réduction) of alkenes

• similar to hydrogénation of alkenes

• Lindlars catalyst is deactivated (poisoned)

• Syn addition results in only the z or cis isomer

Halogénation of alkenes

• bromination adds one Br to each alkene carbon c

• The result is dibromoalkane

Classifying alcohols

• primary when attached to carbon attached to one another carbon

• Secondary when attached to carbon attached to two other carbons

• Tertiary when attached to carbon attached to three other carbons

Oxidation

Gain an oxygen or lose two hydrogens

Réduction

Lose an oxygen or gain two hydrogens

Primary alcohol oxidation

1. Aldéhyde

2. Carboxylic acid

Requires oxidizing agent

Secondary alcohols oxidation

• requires oxidizing agent

• Turns into ketone

Tertiary alcohol oxidation

• a Carbon bond would have to break for oxidation to occur

• Therefore, no reaction

Oxidizing agents

• usually metals in high oxidation states (transfer 2 to 4 electrons)

• I.e mno4, cr2o7 2-,

• Usually done in acid or base to facilitate electron transfer

• Pyridinum chlorochromste (PCC in CH2Cl2) is specific to oxidizing secondary alcohol to ketone does one step only

Reduction of carbon double bond vs carbon double bonded to oxygen group

*Fifure Otto Stefan

Structure of sodium borohydride nabh4

• source of nucleophillic hydrogen that can be used in carbonyl reduction reactions

• Since hydrogen is more electronegative than boron, it holds most of the negative charge on nabh4

• Sodium behaves as a counter ion spectator in borohydride reduction reactions

Désignation of saturated carbon center as 1,2,3,4

Based on how many other carbon atoms it is bonded to

• Valence bind theory

• electrons reside in quantum mechanical orbitals localized on individual atoms

• Orbitals could be atomic SPDF or hybridized ie sp3 sp2 sp

• A chemical bond results from the overlap of two half filled orbitals in which the electrons have opposite spins

• The shape of the molecule is determined by the geometry of the overlapping orbitals

Hybridization

• mix two or more standard atomic orbitals to form new hybrid orbitals

• I.e sp orbitals

• Minimizes energy of molecule by maximizing orbital overlap in a bond

VSEPR vs hybrid orbitals

Rules of hybridization

1. The number of standard atomic orbitals mixed together is equal to the number of hybrid orbitals formed

2. The combination of standard atomic orbitals mixed together determines the shapes and energies of the hybrid orbitals formed

Hybrid orbitals

• hybrid means something of mixed origin or composition

• Hybrid orbitals arise by combo of atomic orbitals

• Upon hybridization

• Total number of orbitals is conserved

• Orbital energy is conserved

• The average energy of the electrons in hybrid orbitals is higheR compared to electrons in atomic orbitals

• Hybridization results in slightly higher potential energy thus would not happen at zero kelvin

Counting number of sigma bonds

• count each single bond

• Count each double bond

• Count each triple bond

Counting pi binds

• count number of double bonds

• Count triple bonds and multiply by 2

Sigma bond

• orbitals overlap end on

• Electron density along inter nuclear axis

• Only one sigma bind possible between two atoms

• Generally stronger and harder to break

Pi bond

Orbitals overlap side on

Nodal plane along internuclear axis

Up to two pi bonds possible between two atoms

Generally weaker and easier to break

Single bond vs double bond

• single bond can have different conformations and the atom arrangement can be changed by rotation about single without breaking any bonds

• Double bonds have different configurations resulting from, spatial arrangement of bonds

• Changing atom arrangement requires breaking the pi bond

• Restricted rotation

Chemistry if vision

• rods and cones contain proteins bound to 11-cis-retinal

• Light stiles the molecule breaking the pi bond

• Sigma bond stays intact allowing for rotation

• Different shape of trans retinal causes changes in the bound protein. And a signal is transmitted to the brain

Melting point of fatty acids

• linear chain close packing with many IMF means highest melting point

• Kinks from tnrans double bonds reduce packing efficiency lower melting point

• Cis double bonds interfere with packing and IMF meaning lowest melting point

E/Z nomenclature

E higher priority groups ch3 are on opposite sides of the double bond

Z higher priority groups ch3 are on the same side of the double bond

For molecules w different groups attached to carbon double bond e/z used instead of cis/trans

Can-Ingold-Prelog rules

• use atomic number to define priority for each pair of atoms bound to each carbon in the carbon double bond

• F9 higher than n7

• Relationship between two high priority groups defines the configuration.

• Opposite sides means e

• Same sides means Z as in together

• When groups are different but have identical atoms bound to c double c, move on to each atom connected to that atom until a point of difference is found

Brainwashing bees

• QMP queen mandibular pheromone causes young workers to feed and groom her

• Suppresses new queens controls colony behaviour

• Contains homovanillyl alcohol or HVA suppresses bad memories but not good ones

• Hypothesis: HVA mitigates unpleasant side effects of QMP

• HVA Lowers dopamine associated with learning

• HVA molecules can treat high dopamine psychoses and schizophrenia

• But needs high specificity (ADHD and Parkinson’s linked to low dopamine) could lead to undesired side effects

When will a molecule have no geometric isomers

if two substituents on a given carbon atom are identical. 2-methyl-2-butene does not have any E- or Z-isomers, because the substituents on carbon #2 are identical (both methyl groups):

Statement “In alkenes the unhybridized p-orbitals form a π-bond and force the substituents attached to the alkene C atoms to become eclipsed.” is correct. The electrons in 2p orbitals of two carbons overlap to form a π bond. When addition happens, it is usually syn addition (same side of p orbital), and thus the substituents on two carbons “overlaps” with each other. This is the eclipsed conformation (high energy, not favored). It will then quickly change to staggered conformation.

True

Statement “sp-, sp²-, and sp³-hybridized orbitals can sometimes form π-bonds”

is incorrect. Only unhybridized p orbitals can form π bond because geometrically they are perpendicular to all the hybridized orbitals.

What makes up a pi bond

Sideways Overlap of p orbitals not sp or s!!!

Hybrid orbitals containing two electrons (a lone pair) cannot participate in forming covalent bonds. This is false. For example, the oxygen atom in water is sp³ hybridized, with each lone pair of electrons on oxygen occupying an sp³ hybrid orbital. The lone pair is attracted to and can form a covalent bond with a carbocation, as shown below.

Yeah false

• The px, py, and pz orbitals are all at 90° angles from one another — like the x, y, and z axes in 3D space.

• Since the σ bonds used px, the π bonds are using py and pz, which are at 90° to each other.

Remember that!

Acid-catalyzed hydration of an alkene goes through the least highly substituted carbocation intermediate” is false. Based on the stability principle of carbocation, the most highly substituted intermediate state will be preferred because it has the lowest activation energy.

Remember

In the formation of a Grignard reagent from an alkyl halide, the carbon atom bearing the halide is reduced.

This statement is true. A Grignard reagent is formed by mixing an alkyl halide with magnesium in diethyl ether. In the original alkyl halide (R₃C–X), the C has a δ+ charge and the X (halogen) has a δ– charge. When Mg inserts between C and X, it generates R₃CMgX, in which Mg has a 2+ charge, X has a 1– charge, and C has a 1– charge. Thus, the oxidation state of carbon has changed from δ+ to 1– => reduction.

Remember

Hydrogenation of alkynes using Lindlar’s catalyst leads to Z - alkenes

Remember!

Hydrogenation occurs via syn addition, in which both hydrogen atoms add to the same face of the alkene, which is a ring in this exampl

Remember that

Combo of one s and three p makes 4 orbitals of equal energy

An isolated p orbital is higher in energy than an sp3 hybrid orbital

carbon typically forms four bonds, and thus has four bonding orbitals, and these bonds are typically single bonds. These bonds are formed through sp3 hybridization, where the four orbitals hybridize from the single 2s orbital and the three 2p orbitals of the carbon atom

In alkenes the unhybridized p-orbitals form a -bond and force the substituents spacedi ted alias atons to become elin sp hybridized