CH 108 Lab Midterm
Comment on the reactivity of ethanol, 2-propanol, and t-butyl alcohol
Most reactive: Ethanol (primary) Least reactive: T-butyl alcohol (tertiary)
Structural differences: Saturated v. unsaturated hydrocarbons
Saturated: No multiple bonds Unsaturated: 1+ multiple bonds
Solubility differences between alcohols
Small alcohols - high solubility Longer alkyl chains - less soluble More hydroxyl groups - more soluble
Structural differences: Straight-chain v. cyclic hydrocarbons
Straight-chain: All carbons are lined up in a row Branched: 1 or more branches come off the main carbon chain Cyclic: Carbons form a ring rather than a chain
Predict the solubility of 1-butanol, 2-butanol, & t-butyl alcohol in water and acetone.
1-butanol: Most water-soluble/most reactive 2-butanol: Moderately soluble T-butyl alcohol: Least solubke
T-butyl alcohol
2-methyl-2-propanol Will not oxidize
Aliphatic
A compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings
Glycosidic bond
A glycosidic bond is a covalent bond in which a carbohydrate binds to another group, which could also be a carbohydrate. A glycosidic bond is found between the two glucose molecules in maltose. * Present in reducing sugars * Makes it possible for the ring to open and form an aldehyde, which can be oxidized to a carboxylic acid
Non-reducing sugar
A sugar which cannot serve as a reducing agent. An example is sucrose.
Solubility of acetic acid, benzoic acid, acetamide
Acetic acid - soluble (would be less soluble if R group was bigger)
Reaction of alkanes/alkenes/alkynes/aromatics with bromine
Add 5% bromine solution to each test tube: methane (gas), acetylene (gas), cyclohexane, toluene Gaseous: Observe immediate reactions, then set in the dark for 5 min and observe again. Use blue litmus paper to test for formation of HBr. Liquid: Note immediate reactions. Hexane - stays orange-red, acidic [Alkanes should not react unless exposed to UV light] Hexene - turns clear, neutral [Alkenes should turn colorless & form HBr - acidic] Cyclohexane - turns clear, weak acid [Alkynes should turn clear and form HBr - acidic] Toluene - stays orange-red, weak acid [Benzene should not react unless Lewis acid catalyst]
Structural differences between aldehydes & ketones
Aldehydes - carbonyl carbon bound to an H atom & an R group Ketones - carbonyl carbon bound to 2 R groups
Differences in reactivity between aldehydes & ketones
Aldehydes are more reactive, due to being more polar Ring structures (ex. benzaldehyde) less reactive
Hydrocarbons that do not contain a benzene ring are known as ...
Aliphatic
Reactivity of aliphatic aldehydes vs. aromatic
Aliphatic aldehydes react more readily than aromatic
Structural differences: alkanes, alkenes, alkynes
Alkanes: No multiple bonds (CnH2n+2) Alkenes: Double bonds (CnH2n) Alkynes: Triple bonds (CnH2n-2)
Cycloalkanes have molecular formulas that are identical to _____.
Alkenes
Test for alcohol solubility
Ethanol, 2-propanol, t-butyl alcohol Test each alcohol by adding them to 2 mL of solvent (water or acetone) until no longer soluble. RESULTS: Ethanol - Most Soluble (smallest molecules) 2-Propanol - Moderately Soluble T-butyl alcohol - Least Soluble (largest molecules) All soluble in acetone.
Structural differences of primary, secondary, tertiary alcohols
They differ by the # of carbons attached to the hydroxyl-bearing carbon * Primary = 1 carbon * Secondary = 2 carbons * Tertiary = 3 carbons
Potassium permanganate (KMnO4) can be used to oxidize aromatic alkanes to carboxylic acids. In the experiment that you are going to do, which compound should produce a carboxylic acid when it reacts with KMnO4?
Toluene
2-propanol
isopropyl alcohol Oxidize to ketone
Toluene
methylbenzene
Classes of carbohydrates
monosaccharides, disaccharides, polysaccharides
anomeric carbon
only carbon attached to two oxygens -OH may point up or down * Sugar will not act as a reducing agent (not readily oxidized)
Amines
organic compounds with an amino group Primary - N bonded to 2 H and 1 hydrocarbon Secondary - N bonded to 1 H and 2 hydrocarbons Tertiary - N bonded to 3 hydrocarbons
Structures of carboxylic acids, amides, amines
Carboxylic acids - At least 1 carboxyl group, very polar (both C-O bonds and O-H bond) Amides - The H from the hydroxyl portion of the carboxyl group is replaced by -NR2 (amine) Amines - Ammonia in which 1 or more H atoms are replaced with hydrocarbon side chains
Differences in reactivity: carboxylic acids, amides, amines
Carboxylic acids - can donate a proton, and H bond even after the proton is donated Amides - Do not donate protons, but can H bond if its R group allows it Amines - can accept a proton from an acid
Benzene
Consists of a ring of six carbon atoms with alternating single and double carbon-carbon bonds. Very stable
Aromatic
Cyclic hydrocarbon that contains pi bonds arranged so that electrons in the p orbital can interact with each other (conjugation)
Lucas' oxidation for secondary and tertiary alcohols
Ethanol, 2-propanol, t-butyl alcohol Add Lucas reagent to each alcohol. Shake vigorously, and record the time it takes to react. Positive = cloudy = Secondary (slow) or Tertiary (rapid) Alcohol RESULTS: Ethanol: - (clear) 2-Propanol: + (cloudy, delayed) T-butyl alcohol: + (cloudy, instant)
Jones' oxidation for primary and secondary alchols
Ethanol, 2-propanol, t-butyl alcohol Dissolve alcohols each in 1 mL of acetone. Add Jones reagent (Kr3Cr2O7) & observe. Positive = Color change from green to orange = Primary or Secondary Alcohol RESULTS: Ethanol: - (green) 2-Propanol: + (yellow?) T-butyl alcohol: + (orange)
Reducing sugar
Can be oxidized Has free aldehyde or ketone group All monosaccharides are reducing sugars
General formula of carbohydrates
C(H2O)n
Acetylene
C2H2 (ethyne) Unsaturated = reactive
Ethanol
C2H5OH Oxidize to aldehyde > carboxylic acid
Cyclohexane
C6H12 Saturated = Not very reactive
Methane
CH4 Saturated = Not very reactive
The reaction of calcium carbide (CaC2) with water (H2O) produces an acetylene (C2H2) molecule. What is the other product? (Hint: Account for all of the atoms not used to make the first product). CaC2(aq) + 2 H2O(l) → C2H2(g) +
Ca(OH)2 (calcium hydroxide)
DNP Test
Lab: Aldehydes & Ketones lab Overview: DNP reacts with carbonyl groups, producing a color change. Reacts with all aldehydes & ketones, but reacts differently for aromatic and aliphatic aldehydes. A "carbonyl" test. Procedure: Add aldehyde/ketone to test tube. Add 10% ethanol. Add DNP and shake gently. Positive: Precipitate forms (aromatic aldehydes show some delay) Results: Acetone - Precipitation Cyclohexanone - Precipitation Butyraldehyde - Mild precipitation, light orange Benzaldehyde - Most precipitation, bright orange (more delay)
Iodoform Test
Lab: Aldehydes & Ketones lab Overview: Iodoform solution reacts with methyl ketones, forming a yellow solid. Differentiates methyl ketones from larger ketones. (Methyl ketone test) Procedure: Add aldehyde/ketone to test tube. Add iodoform solution and swirl gently. Add 10% NaOH. Results: Acetone - Yellow precipitate All others - No precipitate
Chromic Acid Test
Lab: Aldehydes & Ketones lab Overview: Oxidizing agent reacts with aldehydes, changing color. (Aldehyde test) Procedure: Add aldehyde/ketone to test tube. Add acetone. Add chromic acid reagent and shake gently. Positive: Changes color from orange to green-blue (benzaldehyde more slowly) Results: Acetone: - Cyclohexanone: - Butyraldehyde: + Benzaldehyde: + (delay)
Test: Insolubility of carboxylic acids
Lab: Exploring & Identifying Carboxylic Acids, Amines, and Amides Overview: Procedure: Add deionized water to test tubes. Add the carboxylic acids and amides, and observe. Add NaOH and observe. Add HCl and observe. Positive: Results:
Test: Solubility of carboxylic acids
Lab: Exploring & Identifying Carboxylic Acids, Amines, and Amides Overview: Procedure: Add deionized water to test tubes. Add the carboxylic acids or amides. Add NaHCO3. Observe. Positive: Soluble Results: Acetic: + Benzanoic: -
Test: Primary, Secondary, Tertiary Amines
Lab: Exploring & Identifying Carboxylic Acids, Amines, and Amides Overview: Procedure: Add the amines to the test tubes, and note odor. Add benzenesulfonyl chloride to each test tube. Add NaOH, stopper and shake vigorously. Test the pH and if it becomes acidic, add more NaOH. Reaction is complete when oily benzenesulfonyl chloride and smell are gone. Record results. Next, add HCl until solution is acidic. Positive: Precipitate forms Results: AFTER NAOH Primary: - Secondary: + Tertiary: + AFTER HCL Primary: + Secondary: + Tertiary: -
Test: Amides
Lab: Exploring & Identifying Carboxylic Acids, Amines, and Amides Overview: Procedure: Add the carboxylic acids or amides to the test tubes. Add NaOH. Place in hot bath. Measure with red litmus paper, and observe. Positive: Results:
Benedict's test
Lab: Exploring and Identifying Carbohydrates Overview: Determines whether reducing sugar is present (ketoses > aldoses). WIll be positive for all aldose monosaccharides and alpha-hydroxy ketones. If negative - non-reducing sugar Procedure: Add Benedict's reagent to test tubes. Add 5 drops of each carb to the correct tube. Place tubes in boiling water bath. Remove and observe results. Positive: Color change from blue to orange (Aldehyde oxidized to carboxylic acid). Results: Glucose: + Fructose: + Sucrose: - Lactose: +
Barfoed's test
Lab: Exploring and Identifying Carbohydrates Overview: Differentiates mono- and disaccharides. Ketoses will be negative. Procedure: Add Barfoed's reagent to each tube. Add carbohydrates to the correct tube. Place the tubes in boiling water bath. Observe results at 0 min, 1 min, and 2 min. Positive: Both mono- and disaccharides react positively, but monosaccharides much more quickly (2-3 min). Results: Glucose: Fast Fructose: Fast Sucrose: Slow Lactose: Slow Amylose: -
Iodine test
Lab: Exploring and Identifying Carbohydrates Overview: Tests for starch (simple carbohydrates will be negative) Procedure: Add carbohydrates to the correct tubes. Add KI/I2 solurion. Record results at room temperature. Positive: Color change in the presence of iodine (yellow > blue) Results: Glucose: - Fructose: - Sucrose: - Lactose: - Amylose: +
Amides
Organic compounds whose molecules have a carbonyl nitrogen bond. They are the product formed in a reaction between a carboxylic acid and an amine.
What does it mean to be oxidized? What are the possible oxidation products for alcohols? How do these products differ structurally?
Oxidation is the loss of electrons, loss of water, a decrease in C-H bonds, and an increase in C-O bonds Possible products: - Aldehyde: carbonyl group bound to at least 1 H atom - Carboxylic acid: carbonyl group bound to -OH group - Ketones - carbonyl group bound to 2 carbon-containing groups
Reaction of alkanes/alkenes/aromatics with permanganate
Place 10 drops acetone in 3 test tubes. Add 2 drops hexane to a tube, 2 drops hexene to another tube, and 2 drops toluene to the remaining tube. Add 2 drop potassium permanganate to each tube, and record observations Hexane - Dark purple, no precipitate [Alkanes will not react] Hexene - Brown, precipitate [Alkenes will form brown precipitate] Toluene - Burgundy, precipitate [Benzenes will not react without heat]
Oxidation products of alcohols
Primary alcohols - Aldehydes > Carboxylic acids Secondary alcohols - Ketones Tertiary alcohols - None
Reducing agent
The electron donor in a redox reaction. Is oxidized, reduces the species it acts on
