20. Organic HL

Deduce structural formulas for AND apply IUPAC rules for naming compounds containing up to six carbon atoms with one of the following functional groups: amine, amide, ester, and nitrile

*Amines	-NH­2	-ylamine	CH3CH2CH2NH2(Propylamine)
*Amides	-CO-NH2	-anamide	CH3CH2CONH2 (Propanamide)
*Esters	-CO-O-	(Prefix) -anoate	CH3COOCH­3 (Methyl Ethanoate)
*Nitriles	-CN	-anenitrile	CH3CH2CH2CN (Butanenitrile)

Explain why hydroxide is a better nucleophile than H­₂O

Why is OH^- a better nucleophile than H₂O

 The rate at which reactions occur depend on the strength of the nucleophiles. Because OH^- has a negative charge, it will be more attracted to the slightly positive carbocation than neutral water

Describe and explain how the rate of nucleophilic substitution in halogenoalkanes by the hydroxide ion depends on the identity of the halogen

The identity of the halogen (F, Cl, Br, or I). The strongest bonds will be the least likely to react, meaning that weaker halogenoalkanes will react quicker than stronger halogenoalkanes (I > Br > Cl > F)

Describe and explain how the rate of nucleophilic substitution in halogenoalkanes by the hydroxide ion depends on whether the halogenoalkane is primary, secondary, or tertiary

Steric Hinderance- Interference between electronegative alkyl groups and the central carbon. The more alkyl groups there are, the more of a carbocation forming,

Why will tertiary compounds most likely go through the S_N1 Pathway?

Because there is more steric hindrance, there will be a greater positive charge around the carbon. Therefore, the compound will form an intermediate before progressing. Since there is less interference in primary halogenoalkanes, the carbocation will not form

The nature of the halogenoalkanes (1^o, 2^o, 3^o). The S_N1 mechanism is faster than the S_N2 pathway, so tertiary compounds will react faster than secondary, and secondary faster than primary (3^O > 2^O > 1^O).

Describe, using equations, the substitution reactions of halogenoalkanes with ammonia and potassium cyanide

Halogenoalkane + Ammonia à Amine + Acid                     (Heat)

C­₂H₅Cl + NH₃ à C­₂H₅NH₂ + HCl

Halogenoalkane + Cyanide à Nitrile + Salt                          (Heat, Pressure, Catalyst)

C­₂H₅Cl + KCN à C­₂H₅CN + KCl

Explain reactions of primary halogenoalkanes with ammonia and potassium cyanide in terms of the SN2 mechanism

*The group containing nitrogen will be bonded to the alkane at the same time as the halide to represent the transition state. Show these bonds using dotted lines when diagramming. It should be something like this:

Reactants à Transition State à Products

Describe, using equations, the reduction of nitriles using hydrogen and a nickel catalyst

Nitrile + Hydrogen à Amine                                                 (Heat + Ni Catalyst)

C₂H₅CN + 4H⁺ à C­₃H₇NH₂

Describe, using equations, the elimination of HBr from bromoalkanes

Halogenoalkanes + Hydroxide à Alkene                              (Heat, Dissolved in alcohol)

CH₃CH₂Br + OH^- à CH₂CH₂ + HBr + H₂O

Describe and explain the mechanism for the elimination of HBr from bromoalkanes

Elimination Reaction- Mechanism by which halogenoalkanes are dehydrated into alkenes. Uses weak nucleophiles to remove hydrogens and halogens from the hydrocarbon chain, thus desaturating it and introducing double bonds. Requires concentrated OH^- dissolved in an alkali. Two potential pathways:

1.      E_N1 Pathway- Two steps. Similar to substitution, a carbocation intermediate will form before the final product is reached

2.      E_N2 Pathway- One step. Similar to substitution, an incredibly brief transition state will occur as the halogenalkane forms the alkene

Describe using equations, the reactions of alcohols with carboxylic acids to form esters and state the uses of esters

Esterification- the process of creating an ester by combining an alcohol with a carboxylic acid

Alcohol + Carboxylic Acid à Ester +Water                                     (Heat + H₂SO₄)

C₂H₅OH + CH₃COOH à CH₃-CO-O-C₂H₅ + H₂O

Uses of Esters: Perfumes, flavors, solvents, and plasticizers

Solubility- In non-polar substances (fats)

Deduce the structures of the polymers formed in the reactions of alcohols with carboxylic acids

Polymerized esters- called polyesters are formed when monomers have two functional groups, thus producing a repeating chain. These are used in fibers and plastic bottles. Example: PET (Terylene)

Describe using equations, the reactions of amines with carboxylic acids

Amide Condensation- the process of creating an amide by combining amines with a carboxyilic acid

Amine + Carboxylic Acid à Amide + Water                                    (Heat)

CH₃NH₂ + CH₃COOH à CH₃CONH(CH₃) + H₂O

***A Primary Amine forms a Secondary Amide

***A Secondary Amine forms a Tertiary Amide

Deduce the structures of the polymers formed in the reactions of amines with carboxylic acids

Polymerized amides, also called nylon is formed from monomers with two functional groups to produce a repeating chain. These are used for fibers in clothing, carpets, and ropes. Example: 6,6-nylon.

Outline the economic importance of condensation reactions

Condensation Reaction- A combination reaction between two substances that produces a relatively large product and a relatively small molecule

            Examples of small molecules- Mostly H­₂O, but can be both HCl and NH₃

           

Biological example of polyamides- Proteins

Industrial uses: Perfumes, flavors, solvents, and plasticizers

Deduce reaction pathways given the reactants and materials

Describe stereoisomers

Stereoisomers- compounds with the same structural formula but with different arrangements of atoms in space

Describe and explain geometrical isomerism in non-cyclic alkenes

Geometric Isomers- Have functional groups on the same or opposite sides due to a π-bond restricting rotation (in a double bond)

Cis-isomers- Molecules with functional groups on the same side. They have higher BPs and lower MPs

THINK: sisters (cis-ters) stick together

THINK: They’re trans-ported to opposite sides

The more polar isomer is Cis, because the net polar charge is pulling in the same direction.

The more reactive isomer is Cis because the functional groups are closer.

Describe and explain geometrical isomerism in C₃ and C₄ cycloalkanes

Cycloalkanes can have cis and trans isomers as well because the locked ring prevents rotation

            Cis-Cycloalkanes- Have functional group on same side of ring plane

            Trans-Cycloalkanes- Have functional group on sides of ring plane

Explain the difference in physical and chemical properties of geometric isomers

The more polar isomer is Cis, because the net polar charge is pulling in the same direction.

            The boiling point will be higher in cis-compounds for this reason

Example: cis-1,2 dichloroethene has a higher boiling point than it’s trans- counterpart

The more reactive isomer is Cis because the functional groups are closer. Compounds may react differently when heated

            Example: cis- and trans-but-2-ene,1,4-dioic acid reacts differently under heat

Describe and explain optical isomerism in simple organic molecules

Optical Isomers- Compounds composed of a carbon atom bound to four R- groups that are non-superimposable, but in fact mirror images of one another

Enantiomers- Two isomers that are mirror images of one another

            ***MOLECULES ARE ASYMMETRICAL

            Racemic mixture- solution containing both enantiomers in equal concentrations

Chiral carbon- The central carbon bound to four different R-group. The “central atom” of both enantiomers.

Outline the use of a polarimeter in distinguishing between optical isomers

§         Sample solution is placed in a tube

§         Ordinary light is passed through a polarizer which filters all light that is   not going at a specific angle. This becomes plane polarized light

§         Light passes through the sample tube, which is bent by the chemicals being studied

§         Light then hits a second polarizer called an “analyzer” which is rotated until the light passes through it

§         The angle of rotation is recorded

§         Each substance will bend the light to a different angle.

o     Pure samples of enantiomers will rotate light to the same magnitude, but in opposite directions

o     Racemic mixtures will negate each other and cause no rotation

Compare physical and chemical properties of enantiomers

Physical and Properties of Enantiomers- None different except for plane-polarized light

Chemical Properties of Enantiomers- No difference unless they react with another optical isomer, in which case the molecules could have a bearing on the final result, as is the case in numerous biological systems

Example- One enantiomer smells like oranges, the second like lemons