CHEM 127 Lecture Notes - Lecture 1: Sodium Methoxide, Sodium Ethoxide, Sodium Hydroxide

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Chemistry 8.1-8.11

8.1

Elimination reaction: involves loss of elements from the starting material to form a new Pi

bond in the product

- Alkyl halides undergo elimination reactions with Bronsted-Lowry bases. The element

HX are lost and an alkene is formed.

Dehydrohalogenation: removal of the elements of HX, one of the most common methods to

introduce a Pi bond and prepare and alkene.

- It is an example of Beta elimination because it involves loss of elements from two

adjacent atoms: the sigma carbon bonded to the leaving group X, and the Beta

carbon adjacent to it.

- Common bases used in Dehydrohalogenation: Sodium hydroxide, potassium hydroxide,

sodium methoxide, sodium ethoxide, potassium tert-butoxide

- To draw any product of dehydrohalogenation:

1) Find the sigma carbon-the sp3 hybridized carbon bonded to the leaving group

2) Identify all Beta carbons with H atoms

3) Remove the elements of H and X from the sigma and beta carbons and form a

Pi bond

8.2

- The sigma bond, formed by end-on overlap of the two sp2 hybrid orbitals, lies in the plane of

the molecule

- The Pi bond, formed by side-by-side overlap of two 2p orbitals, lies perpendicular to the plane

of the molecule. The pi bond is formed during elimination

Monosubstitued alkene: has one carbon atom bonded to the carbons of the double bond.

Disubstituted alkene: Has two carbon atoms bonded to the carbons of the double bond and so

forth

- The cis isomer has two groups on the same side of the double bond

- The trans isomer has two groups on opposite sides of the double bond

- Trans alkenes are generally more stable than cis alkenes

Diastereomers: Stereomers, but not mirror images of each other

Whenever the two groups on each end of a carbon-carbon double bond are different from

each other, the two diastereomers are possible

- The stability of alkenes increases as the number of R groups bonded to the double bond carbons

increases

- R groups increase the stability of an alkene because R groups are sp3 hybridized,

whereas the carbon atoms of the double bond are sp2 hybridized.

- sp2 hybridized carbon atoms are more able to accept electron density and sp3 hybridized

carbon atoms are more able to donate electron density

- Increasing the number of electron-donating R groups on a carbon atom able to accept electron

density makes the alkene more stable

- Trans alkenes are more stable than cis alkenes cause they have fewer steric interactions

- Increasing alkyl substitution stabilizes an alkene by an electron-donating inductive effect

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Document Summary

Pi bond the molecule forth adjacent atoms: the sigma carbon bonded to the leaving group x, and the beta carbon adjacent to it. Alkyl halides undergo elimination reactions with bronsted-lowry bases. It is an example of beta elimination because it involves loss of elements from two. Common bases used in dehydrohalogenation: sodium hydroxide, potassium hydroxide, Elimination reaction: involves loss of elements from the starting material to form a new pi bond in the product. Dehydrohalogenation: removal of the elements of hx, one of the most common methods to introduce a pi bond and prepare and alkene. The sigma bond, formed by end-on overlap of the two sp2 hybrid orbitals, lies in the plane of. The pi bond, formed by side-by-side overlap of two 2p orbitals, lies perpendicular to the plane of the molecule. Monosubstitued alkene: has one carbon atom bonded to the carbons of the double bond.

Related Questions

Â¥Write a brief (less than 150 words, 3 or 4 sentences) of the aim of the experiment

Â¥Address question of what was done, how it was done, and what compounds were used.

Â¥Include Chemical Reaction where relevant.

See text below. Please provide Purpose following the steps above. Thank you.

Alcohols R-O-H are characterized by the presence of the hydroxyl group

Because of intermolecular co-association, alcohols show higher boiling points

than aldehydes, ethers, or ketones of similar mass. Among alcohols, boiling

points increase with increased surface area. Increased surface area occurs as

more carbons are added to the alkyl portion or with decreased branching of th

alkyl group. Thus, 1-propanol has a higher boiling point than ethanol

(increased C#). 1-propanol also has a higher boiling point than 2-propanol

(decreased branching)

The solubility of alcohols in water decreases as the surface area of the

alkyl (nonpolar) portion increases. Thus, alcohols become less soluble in water

as the number of carbons in the alkyl group increases. When comparing

alcohols that contain the same number of carbons, branching of the alkyl group

decreases its surface area and thus increases the water solubility of the alcohol.

1-Propanol is slightly soluble in water while 2-propanol is quite soluble

The limit of water solubility is reached at about 4 or 5 carbons in the

alkyl group. However, it is possible to "salt out" or separate a water-soluble

alcohol from the water it is mixed with by the addition of certain salts such as

K2CO3. If an alcohol-water mixture is saturated with such a salt, the anion

selectively forms strong ion-dipole bonds to water, leaving the alcohol as a

separate layer. Thus, water is separated from the alcohol because the ionic salt

bonds more strongly with water than with the alcohol. There are twice as many

ion-dipole bonds possible with water than with the alcohol.

Alcohols are relatively acidic organic molecules, being weaker acids than

water, yet stronger than acetylene.

Acidity: water > alcohol > acetylene > ammonia > alkanes

Alcohols may be converted to sodium alkoxides by the action of metallic sodium

under anhydrous conditions. Primary alcohols react more readily tharn

secondary or tertiary alcohols due to the relative stability of the alkoxide ions in

the solvent alcohol.

R-o:-

Alcohols undergo nucleophilic substitution reactions with ease under

acidic conditions. The relative ease of such substitution for primary, secondary

and tertiary alcohols serves as a means of classification. Upon treatment with

concentrated HC1, tertiary alcohols are rapidly converted to alkyl chlorides

Secondary alcohols require warming in a boiling water bath for 15 minutes

Primary alcohols do not react at all under these conditions. The alkyl chlorides

formed by this reaction are insoluble in the concentrated HCl and form an

easily detectable second layer

R-O-H HC1 >

Ð-Ð-Ð

Complications arise from the fact that benzylic and allylic alcohols also

react immediately, but yield products that are soluble in the concentrated HCI

Alcohols are easily oxidized by any of these strong oxidizing agents:

dilute KMnO4, NajCr.07 in acid, or CrO3 (chromic anhydride)

acidified sodium dichromate is somewhat helpful in the classification of

alcohols. Prim

ary and secondary alcohols are oxidized rapidly within several

minutes, while tertiary alcohols do not react under these conditions

Oxidation occurs more easily when the carbon bearing the -OH group

bonded to at least one atom of hydrogen. The complex mechanism of

involves the transfer of a hydride ion H:- as a critical step.

hydrogen atom is absent (as in tertiary alcohols), no oxidation can occur

directly. Tertiary alcohols may be oxidized indirectly through the formation of

Alcohols which contain the partial structure C- CH3 give positive

Ð¾Ð½

results in the iodofora reaction. When the alcohol is dissolved in water and

KOH, the addition of a solution of 12 in KI yields a yellow precipitate of

iodoform, CHI3, along with the oxidized portion of the alcohol

Hypoiodite ion is produced by the reaction between molecular iodine and

hydroxide ion:

I2 + 4(OH) -

The hypoiodite ion in turn oxidizes an alcohol with the proper structure

Once this oxidation has occurred, additional hypoiodite ion continues to

react with the aldehyde or ketone produced:

CH,-C

3 (0I)-IC-c3 (OH)-

resulting in the final substitution reaction to give iodoform and the anion of a

carboxylic acid containing one carbon atom less than the original alcohol:

128

lodoform precipitates as fine yellow crystals. This precipitate, a result of a

specific oxidation followed by a substitution, is an indication of the partial

structure of the original alcohol.

Simple alcohols of up to ten carbon atoms may be detected by the

ammonium hexanitrocerrata(lV) reagent, (NH4Ce(NO,). The hexanitro-

cerrate(IV) ion has a distinctive orange-red color. When an alcohol, ROH is

added, one or more OR- groups replace the nitro groups as ligands in the

complex ion. The new complex ion formed has a distinctive color. The general

equation for this reaction is:

This test is positive for aliphatic alcohols up to approximately ten carbons in

length. Phenols or larger alcohols yield insoluble mixtures

Alcohols react with acids or with acid derivatives to form esters. This

characteristic reaction is useful in the formation of specific esters such as ethyl

acetate, acetylsalicylic acid (aspirin) and methyl salicylate (oil of wintergreen). In

this experiment, methyl salicylate will be prepared by reacting methyl alcohol

with salicylic acid in the presence of a trace of sulfuric acid as the catalyst

Lower molecular weight alcohols such as ethanol, methanol, and

isopropyi alcohol absorb water on exposure to moist air or are prepared as

azeotropic mixtures containing water. The presence of water in alcohols may be

detected in several ways. If a small lump of CaC2 is added to any alcohol that

contains a trace of water, a reaction occurs that produces immediate bubbles of

acetylene gas:

Thus, evolution of acetylene gas upon the addition of calcium carbide indicates

the presence of water in the alcohol. Another way to test for the presence of

water in alcohols involves the use of anhydrous cupric sulfate powder (CuSO4)

Anhydrous cupric sulfate is a very pale, almost white powder. In the presence of

water, deep blue crystals of cupric sulfate pentahydrate,

CuSO4-5H20, are formed. Thus, anhydrous cupric sulfate indicates the

presence of water in an alcohol by a simple color change.

Commercial ethanol is produced as an azeotropic mixture that contains

95% ethanol and 5% water. Absolute alcohol contains no water. Many reagent

grade alcohols are composed of a nonpotable mixture of 95% ethanol and 5%

isopropyl alcohol. Thus, absolute ethanol and reagent alcohols are both water

free and give negative results when tested for the presence of water

Test 1-Multiple Choice: Choose and underline the best answer in each of the following statement/question.

_____1. Which of the following best differentiates an aldehyde from a ketone?

a. In aldehydes, carbon is bonded to a hydroxyl group.

b. In aldehydes, hydrogen is bonded to an oxygen group.

c. In aldehydes, hydrogen is bonded to a carbonyl group.

d. In aldehydes, oxygen is bonded to an oxygen group.

_____2. Which of statement is not true about petroleum and its products?

a. Petroleum is fossil fuel.

b. Petroleum is a mixture of hydrocarbons with sulfur as impurity.

c. There is no harm that comes from the use of petroleum products.

d. Petroleum comes from decomposition of materials of living origin.

_____3. Cooking gas or liquefied petroleum gas(LPG) is a mixture of C₃H₈ and C₄H₁₀. Which are these compounds?

a. pentane and butane b. methane and butane

c. propane and butane d. propane and methane

_____4. Which of the following compounds ionizes in water and, thus conducts electricity poorly?

a. acetic acid b. hydrochloric acid c. distilled water d. sodium hydroxide

_____5. A lead storage cell can function both as an electrolytic cell and as a voltaic cell. When a lead storage battery is being recharged, it converts ________ energy to_____--energy

a. chemical : electrical b. chemical to heat c. electrical to mechanical

_____6. The acid electrolyte in a lead storage battery is

a. HCl b. H₂SO₄ c. HNO₃ d. CH₃COOH

____7. The anode and cathode in a dry cell respectively are

a. Zn and C b. C and Zn c. Pb and PbO₂ d. PbO₂ and Pb

____8. What is the proper name for the compound CH₃CH₂CH₃?

a. ethane b. propane c.butane d. pentane

____9. Which of the following is the simplest hydrocarbon?

a. CH₂ b. C₂H₄ c. CH₃ d. CH₄

____10. Hydrocarbons such as CH₂ =CH₂ are said t be

a. ionic b. aromatic c. saturated d. unsaturated

_____11. Which of the following best describes hydrocarbons?

a. flammable ionic compounds that are insoluble in water and are denser than water

b. flammable ionic compounds that are insoluble in water and are denser than water

c. flammable covalent compound that are insoluble in water and are less dense than water

d. flammable covalent compounds that are soluble in water and less dense than water

_____12. Which of the following will result if hexane and water are mixed?

a. an explosion

b. clear solution of hexane dissolved in water

c. a layer of hexane on top of a layer of water

d. a layer of water on top of a layer of hexane

_____13.Which of the following is not a gas?

a. ethene b. octane c. methane d. acetylene

_____14. Which of the following is another name for wood alcohol?

a. methanol b. propanol c. grain alcohol d. rubbing alcohol

_____15. Which of the following alcohols groups are found in beverages?

a. ethyl b. methyl c. denatured d. wood

_____16. Which of the following is the only element present in organic compounds?

a. hydrogen b. oxygen c. carbon d. nitrogen

_____17. Which of the following is chlorofluorocarbon?

a. C₃F₈ b. CHF₃ c. CFCl₃ d. CHCl₃

_____18.What percent of alcohol is present in vodka which is 90 proof?

a. 9 b. 45 c. 90 d. 180

____20. Which of the following is formed when carbohydrates undergo fermentation process?

a. ethanol b. methanol c. glucose d. formaldehyde

_____21. In ethene, the two carbon atoms are joined by a

a.single bond b. double bond c. triple d. ionic

____22. The IUPAC name of CH₃CH₂CHCH₂CH₃ is

CH₂CH₃

a. 3-methylpentane b. 3-ethylpentane c. 2-ehtylpentane d. 2-methylpentane

____23. The IUPAC name of CH₃-O-CH₃ is

a. methoxymethane b. ethylether c. dimethylether d. dimethyloxide

____24. Which is an alcohol?

a. C₆H₆

b. CH₃-C-CH₃

c. CH₃-O-CH₃

d. CH₃OH

____25. A group which both aldehydes and ketones have in common is

a.-C=O b. âOH c. âO- d. -COOH

___26. The aroma associated with this class of compounds is regarded as pleasant.

a. amides b. esters c. carboxylic acids d. ketones

____27. The IUPAC name of CH₃CH₂CHO is

a. propanone b. propanol c. propanal d. propionic acid

____28.The âCOOH group is called

a. aldehyde group b. hydroxyl group c. carbonyl group d. carboxylic group

____29.The alkyl group of butane is

a. C₂H₃ b. C₃H₅ c.C₄H₇ d. C₄H₉

____30. The simplest alkene is

a. CH=CH b. CH₂=CH₃ c. CH₂=CH₂ d. CH₃CH=CH₂

Test 2. Answer the following questions completely.(3 points each)

1.Why are alcohols of lower molecular weight more soluble in water than those with higher molecular weights?

2. Which of the following pairs of compounds has

a. higher bolilng point:1-bromopentane or 1-chloropentane _____________________

b. the greater density: heptanes or octane ______________________
c. the higher boiling point :pentyl alcohol or pentylamine ______________________

d. the higher boiling point: hexylamine or dipropylamine ______________________

3. Explain why each of the following names are incorrect.Give the correct IUPAC name.

a. 3-Butanone

b. 1-Butanone

4. What is unique about carbon atom that makes it form numerous compounds?

5. Acetone or propanone is completely soluble in water,but 4-heptanone is completely insoluble.Explain.

Test 3.. Give the name and chemical formula of the functional group of each of the following organic groups. The first one has been done for you.

Organic Group	Functional chemicalfFormula	Functional group name
1.Alkanes	-C-C-	carbon carbon single bond
2.Alkenes
3.Alkynes
4.Alcohols
5. Aldehydes
6. Ketones
7. Thiols
8. Ethers
9.Carboxylic acids
10.Esters
11. Amines
12. Amides

CHEM 127 Lecture Notes - Lecture 1: Sodium Methoxide, Sodium Ethoxide, Sodium Hydroxide

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