Ochem Lab

theoretical plates

-the point in distillation at which liquid-vapor equilibrium is reached -is a measurement of efficiency of a distillation apparatus 1 simple distillation = 1 theoretical plate 1 fractional distillation = >1 theoretical plate

Miscible

- Describes two liquids that are soluble in each other

Immiscible

- liquids that are not soluble in each other

The presence of a broad peak at 3200 cm-1 is a positive test of what

- positive test indicating the presence of an alcohol

___________ >>>oxidation>>> 2- Heptanone

2- Heptanol

isoprene

The five-carbon units are joined together to form Vitamin A1.

Eclipse Conformation

- A confirmation about a carbon-carbon single bond in which the atoms or groups on one carbon appear to eclipse the atoms or groups on an adjacent carbon when viewing the molecule via a Newman projection •This type of arrangement is the least stable and greatest in energy since the substituents on each carbon are near and eclipse each other, therefore exhibiting the greatest amount of torsional strain

Staggered conformation (anti-periplanar)

- A confirmation about a carbon-carbon single bond in which the atoms or groups on one carbon are as far apart as possible from atoms or groups on an adjacent carbon - lowest energy

Thermal conductivity detector

- A device that detects substances eluted from a gas chromatography column by measuring changes in the thermal conductivity of the gas stream.

Crystallization

- A separation technique that results in the formation of pure solid particles of a substance from a solution containing the dissolved substance

Thin Layer Chromatography (TLC) - Method

- A type of chromatography that uses silica gel or alumina on a card as the medium for the stationary phase - Method to separate out pigments based on solubility

Factors to remember in determination of a melting point

- An impurity usually lowers the melting point of an organic compound. - A eutectic mixture has a sharp melting point. - It is important that the height of the sample in the capillary is only 1-2 mm, and that it be packed firmly. - The lower end of the melting point range is the temperature at which the first drop of liquid is seen. Eutectic mixture: A liquid that can transform between two phases at the same time.

Gas Chromatography (GC) - Method

- Chromatographic procedure in which a mixture of gases or highly volatile liquids is separated using a carrier gas passing through a solid, or viscous liquid on a solid support, packed in a column

Simple Distillation - Method

- The solution is heated. The part of the solution that has the lowest boiling point evaporates first - The vapour is then cooled, condensed & is collected - The rest of the solution is left behind in the flask

all chromatography techniques involve

- a moving phase and a stationary phase

Fundamental mode of vibration examples

- bond stretching - bond bending - bond scissoring - bond wagging

second order reaction (SN2 and E2)

- rate is proportional to either the concentrations of the nucleophile or the substrate

first order reaction (SN1 and E1)

- rate is proportional to either the concentrations of the substrate

Fractional distillation - Method

- separation of a liquid mixture into fractions differing in boiling point (and hence chemical composition) by means of distillation. - typically using a fractionating column.

workup the reaction

- series of manipulations required to isolate and purify the product(s) of a chemical reaction

important requirements for separation of two liquids by fractional distillation:

- sufficient difference in boiling points of components - maintenance of the proper temperature gradient in the column - extensive contact between the liquid and vapor phases - sufficient column length

eutectic point

- the lowest temperature at which the existence of a liquid phase is possible - The point at which the specific proportions of 2 components of a mixture, yields the lowest melting temperature

Oxidation agent

- the substance that oxidizes another substance by accepting its electrons -Becomes Reduced Ex: pyridinium chlorochromate (PCC), NaOCl, KMnO4, and Tollens' NOT: SOCl2

Gauche conformation

-A confirmation about a single bond of an alkane in which two groups on adjacent carbons lie at a dihedral angle of 65°.

Dehydration products

-Alkene and water -Elimination reaction

What test is used to identify the presence of phenols and Enols?

-Ferrous chloride test Positive: purple to reddish-brown to green

TLC plate polarity

-Less polar component travels further than the more polar component

sp hybridization

-Linear (180 degrees) -Two double bonds -one triple bond -Carbon bonded to two other elements

What tests is used to identify halide ions in a solution?

-Silver nitrate Positive test:

Reduction agent

-The molecule that donates electrons to another - Becomes oxidized Ex: NaH, LiH, LiAlH4, and CaH2 (compounds that contain the H− ion) (Some elements and compounds can be both reducing or oxidizing agents.)

Recrystallization - Method

-The process by which bonds between atoms in minerals break and re-form in new ways during metamorphism. -Purify solid compounds that are soluble

sp2 hybridization

-Trigonal planar structure (120 degrees) -One double bond -Carbon bonded to 3 elements

Terpenes

-metabolic precursors to steroids and other lipid signaling molecules -odiferous chemicals -class of lipids built from isoprene - carbons are grouped in multiples of 5 -grouped according to the # of isoprene units present -a single terpene consists of 2 isoprene units

Boiling chips

-small pebbles that are placed in the bottom of the test tube while it is being heated -provide nucleation sites that give the liquid a place to start forming bubbles to prevent superheating -prevents liquid from splattering

anti-periplanar

-substituents are attached to parallel bonds on opposite sides of a molecule -Angel 180 degrees

sp3 hybridization

-tetrahedral (109.5 degrees) -single bonds only -Carbon bonded to four other elements

Which compounds test(s) for Unsaturated molecules in the product? What occurs in a Positive test?

1. Bromine test Positive: brown color of bromine disappears (colorless) 2. Baeyer test (dilute potassium permanganate) Positive: Purple solution turns to brown precipitate

SN1 reaction

1. Leaving group leaves forming a positively charged carbocation (rate-limiting step) *The rate of rxn depends only on the concentration of the substrate rate = k [R-L] R-L is the alkyl group containing the leaving group *Anything that accelerates the formation of the carbocation increase the rate of rxn 2. Nucleophile attacks the carbocation (unstable) *results in substitution product -Product is usually enantiomers

Rf is

Relative flow rate (or migration) on TLC

When is recrystallization not a suitable method to purify an organic material?

When the organic material is a liquid instead of a solid. Suitable Materials include: When the organic material is insoluble in water. When the organic material is thermally unstable near its melting point. When the organic material is impure.

An sp carbon typically has ___ atoms attached to it with bond angles of about ____. a. 2; 180 degree b. 3 ; 180 degree c. 4 ; 120 degree d. 4 ; 109 degree e. 5 ; 109 degree

a. 2; 180 degree

In the determination of a melting point, indicate which of the following statements is false. a. An impurity usually raises the melting point of an organic compound. b. A eutectic mixture has a sharp melting point. c. An impurity usually lowers the melting point of an organic compound. d. It is important that the height of the sample in the capillary be only 1-2 mm, and that it be packed firmly. e. The lower end of the melting point range is the temperature at which the first drop of liquid is seen.

a. An impurity usually raises the melting point of an organic compound.

Carboxylic acids have high retention times on polar GC columns because: a. carboxylic acids interact strongly with the polar column. b. carboxylic acids tend to be fairly volatile. c. non-polar compounds are separated according to boiling points. d. carboxylic acids have a high number of theoretical plates. e. the carrier gas flow for carboxylic acids is usually slow.

a. carboxylic acids interact strongly with the polar column.

In fractional distillation, the efficiency of a distillation column is described by: a. indicating the number of theoretical plates. b. stating the packing material used. c. indicating the volume of distillate obtained. d. comparing the pot to the head temperature. e. the length of the column.

a. indicating the number of theoretical plates.

10. Which of the following laboratory techniques would be preferred for purifying a six-gram sample of 95% benzoic acid? a. recrystallization b. fractional distillation c. gas chromatography d. simple distillation e. thin layer chromatography

a. recrystallization

The Who Has My Compound experiment included a solubility test for the unknown compounds in sodium bicarbonate. What purification technique made use of the same chemical properties as this solubility test? a. recrystallization b. gas chromatography c. distillation d. reverse phase chromatography e. biphasic extraction with a basic solution

a. recrystallization

After we have completed an organic reaction, we often "workup" the reaction. The term "workup" refers to: a. the general method of purification that uses aqueous-organic extraction b. collection of crystals c. the process of distillation d. concentration or removal of the solvent from a reaction e. the addition of a drying agent to a solution of the product

a. the general method of purification that uses aqueous-organic extraction

A phase transfer catalyst: a. transfers a reactant between two different phases b. converts an organic compound to an aqueous compound c. converts an aqueous compound to an organic compound d. separates aqueous compounds from organic compounds faster e. none of these

a. transfers a reactant between two different phases

Many types of chromatography exist, but they all have common characteristics. Which statement is true for any chromatographic method? a. The identity of an unknown compound can be proven by finding that the compound has a retention time or Rf identical to that of a known compound. b. Components of a mixture are separated because of differences in their distribution coefficients between a mobile phase and a stationary phase. c. The amount of each compound in a mixture can be readily determined by any chromatographic method. d. A solvent is always the mobile phase. e. The stationary phases must be enclosed by a column.

b. Components of a mixture are separated because of differences in their distribution coefficients between a mobile phase and a stationary phase.

In the Dehydration of Cyclohexanol experiment, the product (cyclohexene) is obtained by performing which class of reaction? a. Substitution b. Elimination c. Addition d. Radical e. Pericyclic

b. Elimination

Eugenol, an aromatic phenol, may be easily isolated from clove oil by which of the following methods? a. formation of a DNP derivative b. base extraction and neutralization c. steam distillation d. acid extraction and neutralization e. recrystallization

b. base extraction and neutralization

The class of natural products called terpenes are derived from which repeating subunit? a. styrene b. isoprene c. ethylene d. Acetyl e. cyclohexyl rings

b. isoprene

Which of the following variations of 1,2-dimethylcyclohexane in the chair conformation is the most stable? a. methyl groups are diaxial b. methyl groups are diequatorial c. methyl one is axial, methyl two is equatorial d. methyl one is equatorial, methyl two is axial e. all are equally stable since it is in the chair conformation

b. methyl groups are diequatorial

Which of the following techniques would not induce crystallization? a. thorough chilling of the solution b. slowly warming the cold solution c. slow cooling of the solution to room temperature d. scratching the side of the beaker at the liquid line e. introducing a seed crystal to the solution

b. slowly warming the cold solution

In thin-layer chromatography, Rf is a. the number of spots on the TLC-plate b. the ratio of the distance the spot moves from the origin to the distance the solvent moves from the origin c. the distance from the origin to the solvent front minus the distance the spot travels d. a number greater than 1 e. a ratio that allows for determination of molecular weight

b. the ratio of the distance the spot moves from the origin to the distance the solvent moves from the origin

Which of the following is characteristic of a good recrystallization solvent? a. the solvent reacts with the sample b. the solvent boils below the melting point of the sample c. the sample is highly soluble in the solvent at low temperature d. the sample is slightly soluble in the solvent at high temperature e. the solvent is nonvolatile

b. the solvent boils below the melting point of the sample

In the lowest energy "gauche" conformation of butane calculated by the computer, the dihedral angle between the two methyl groups was a. 35 degrees b. 45 degrees c. 65 degrees . d. 60 degrees e. 185 degrees

c. 65 degrees

Acetone is not suitable as a solvent for the extraction of organic materials from water because a. Acetone is not a good solvent for organic materials. b. Acetone is not sufficiently volatile to allow for recovery of the product. c. Acetone and water are miscible. d. Acetone reacts with organic compounds so it is used to remove organics from glassware. e. Acetone is too low boiling to be used for extraction.

c. Acetone and water are miscible.

What type of detector is used in the GC instruments used in the TAMU Organic I Teaching Labs? a. UV absorbance detector b. FTIR detector c. Thermal conductivity detector d. Flame ionization detector e. Ionic detector

c. Thermal conductivity detector

The rate of a chemical reaction is important: a. because it provides data on the heat of reaction b. because it gives the acceleration of a reaction c. for determining the mechanism of a reaction d. as an indication of the type of products produced e. as a measure of a reaction progress

c. for determining the mechanism of a reaction

An IR spectrometer: a. measures the emission of infrared radiation by various functional groups. b. can only detect organic compounds. c. measures absorption of infrared radiation by various functional groups. d. can only be used with samples that are liquids. e. cannot be used for quantitative analysis.

c. measures absorption of infrared radiation by various functional groups.

Which of the following is not an important requirement for the satisfactory separation of two liquids by fractional distillation? a. sufficient column length b. extensive contact between the liquid and vapor phases c. sufficient difference in densities of components d. maintenance of the proper temperature gradient in the column e. sufficient difference in boiling points of components

c. sufficient difference in densities of components

The eutectic point is: a. the melting point of a pure compound b. the melting point of a mixture of 50% A and 50% B c. the lowest melting point for a mixture of A and B d. the highest melting point for a mixture of A and B e. none of these

c. the lowest melting point for a mixture of A and B

Phase transfer catalysis can be useful in carrying out reactions in which: a. the reactants are too reactive b. the energy of activation is too low without catalysis c. the reactants are not soluble in the same solvent d. one of the reactants reacts with common solvents e. the mechanism needs to be changed from SN1 to SN2

c. the reactants are not soluble in the same solvent

When you performed simple distillation upon a 50/50 mixture of hexane and octane, you later analyzed your fractions using GC. What was the purpose of performing the GC? a. to determine the molecular weight of the samples b. to determine the boiling points of the components in your samples c. to determine the proportions of hexane and heptane in your samples d. to determine the vapor pressure of the hexane/heptane fractions e. to determine what functional groups were present in the fractions being analyzed

c. to determine the proportions of hexane and heptane in your samples

You develop a TLC plate and view it under UV light. You see no spots. You should: 1. assume your compound is not UV active 2. assume that you didn't get enough sample on the plate, so you re-spot and redevelop that same plate 3. leave the TLC plate in the chamber longer the next time 4. assume that you spotted too much sample on the plate a. 2 and 3 b. 1, 3 and 4 c. 4 only d. 1 only e. 3 only

d. 1 only

An sp3 carbon typically has _____ atoms attached to it with bond angles of about ______. a. 3 ; 180 degree b. 4 ; 120 degree c. 5 ; 109 degree e. 2 ; 180 degree d. 4 ; 109 degree

d. 4 ; 109 degree

Which of the following statements is/are true about the SN1 reaction of 1-phenyl-1-chloroethane in water/ethanol? I. Carbocation formation is the rate-determining step. II. Addition of water is the rate-determining step. III. The product is a mixture of enantiomers.

d. I and III only

Which structure below represents the lowest energy conformation of butane?

d. Staggered conformation (anti-periplanar)

Which statement is false about the phase transfer reaction? a. the phase transfer catalyst is a quaternary ammonium salt b. the naphtholate anion is water-soluble c. allyl bromide is soluble in organic solvents d. one method of changing the solubility of the reactant ion is to pair it with a hydrophobic counter ion e. this reaction takes place in a homogenous solution

e. this reaction takes place in a homogenous solution

IR spectroscopy and classification tests were utilized in the dehydration of the cyclohexanol experiment. What would you expect from the IR spectrum and the classification tests to indicate a successful experiment? a. The presence of a broad peak at 3200 cm-1 and positive tests indicating the presence of an alcohol b. The presence of a broad peak at 3200 cm-1 and positive tests indicating the presence of an alkene c. The presence of a broad peak at 3200 cm-1 and positive tests indicating the presence of a ketone d. The absence of a broad peak at 3200 cm-1 and positive tests indicating the presence of an alkene e. The absence of a broad peak at 3200 cm-1 and positive tests indicating the presence of an alcohol

d. The absence of a broad peak at 3200 cm-1 and positive tests indicating the presence of an alkene

What is the proper amount of solvent to use for recrystallization? a. enough to dissolve everything at a cool temperature b. enough to dissolve everything at a hot temperature c. add cool solvent dropwise until nothing continues to dissolve upon addition of more solvent d. add hot solvent dropwise until nothing continues to dissolve upon addition of more solvent e. just enough solvent to moisten the surface of the solid so the impurities can wash out

d. add hot solvent dropwise until nothing continues to dissolve upon addition of more solvent

During the Dehydration of the Cyclohexanol experiment, the desired product was distilled as an azeotrope (a mixture that behaves as a pure component and has a single boiling point), what two compounds comprised this azeotropic mixture? a. water and cyclohexanol b. water and ethanol c. cyclohexanol and cyclohexane d. cyclohexene and water e. cyclohexanol and dehydrating acid

d. cyclohexene and water

What is the hybridization of the carbon atom and associated bond angles around carbon in formaldehyde, CH2O? a. sp and 120 degrees c. sp2 and 109.5 degrees e. sp3 and 109.5 degrees b. sp and 180 degrees d. sp2 and 120 degrees

d. sp2 and 120 degrees

49. You have performed all of the following classification tests this semester except a. Bromine test b. Bayer test c. Silver Nitrate test d. Ferrous Chloride test e. Ninhydrin test

e. Ninhydrin test

Which of the following reagents is not an oxidizing agent? a. pyridinium chlorochromate (PCC) b. NaOCl c. KMnO4 d. Tollens' e. SOCl2

e. SOCl2

A dichloromethane solution contains three compounds, A, B, and C. When this dichloromethane solution is extracted with aqueous sodium hydroxide, one obtains a basic aqueous solution of Compound A and a dichloromethane solution of compounds B and C. If this latter dichloromethane solution containing B and C is extracted with aqueous hydrochloric acid, one obtains an acidic aqueous solution containing compound B and a dichloromethane solution containing compound C. Of the following, Compound B is most probably: a. ethanol b. benzoic acid c. dodecane d. sodium sulfate. e. benzocaine

e. benzocaine

Which of the following is not a fundamental mode of vibration: a. bond stretching b. bond bending c. bond scissoring d. bond wagging e. bond rotation

e. bond rotation

The rate of solvolysis of the 1-phenyl-1-chloroethane, R-Cl, with water, is a. second order in H2O b. independent of the amount of R-Cl present c. first order in both H2O and R-Cl d. faster in 50:50 water: ethanol than in 60:40 water: ethanol because of the cationic intermediate is more stable in the 50:50 medium e. independent of the amount of water

e. independent of the amount of water

You have to decide between simple distillation and other methods for the separation of two liquid compounds. For which one of the following cases would you choose simple distillation? a. the compounds have different melting points b. both compounds have the same boiling points c. both compounds boil between 100 and 120 *C d. the compounds form an azeotrope e. one compound is a nonvolatile impurity dissolved in the other liquid

e. one compound is a nonvolatile impurity dissolved in the other liquid

Boiling chips are used to prevent bumping during a distillation because they: a. provide surface area for condensation b. lower the vapor pressure of the more volatile component c. adsorb impurities d. prevent the formation of bubbles e. provide surface area for bubbles to form

e. provide surface area for bubbles to form

As used in the TAMU Organic I Teaching Labs, the Baeyer test (dilute potassium permanganate) is a test for: a. aldehydes d. aromatic hydrocarbons b. carbohydrates c. ethers e. unsaturated hydrocarbons

e. unsaturated hydrocarbons

nonvolatile

liquids that evaporate slowly

Gas Chromatography can determine the ________ of your samples

proportions

A nonvolatile impurity dissolved in a liquid:

raises the boiling point and lowers the vapor pressure