Chemistry of Carbon Compounds Flashcards

Comprehensive practice flashcards covering functional group reactions and conversions in organic chemistry based on Section 11 notes.

What quote from Harry Potter and the Chamber of Secrets appears on the Section 11 lecture notes?

"It is not our abilities that show what we truly are. It is our choices."

How are alkanes defined in terms of saturation and bond structure?

Alkanes are saturated hydrocarbons containing strong C-C and C-H single bonds.

Why are alkanes generally very unreactive?

Because they have strong C-C bonds and C-H bonds.

What reaction condition is required for the complete combustion of an alkane?

Burning under a sufficient amount of air or oxygen gas.

What products are formed during the complete combustion of an alkane?

Carbon dioxide ($CO_2$) and water ($H_2O$).

What type of flame is produced during the complete combustion of an alkane?

A non-sooty, blue (non-luminous) flame.

How is a non-sooty blue flame achieved using a Bunsen burner?

By opening the air hole in the Bunsen burner.

What products are formed during the incomplete combustion of an alkane?

Carbon dioxide ($CO_2$), water ($H_2O$), carbon monoxide ($CO$), and carbon ($C$) (soot).

What type of flame is produced during incomplete combustion of an alkane?

A sooty, orange/yellow (luminous) flame.

How is a sooty orange/yellow flame achieved using a Bunsen burner?

By closing the air hole in the Bunsen burner.

What is the balanced chemical equation for the complete combustion of methane gas?

$$CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)$$

What is the chemical equation given for the incomplete combustion of pentadecane ($C_{15}H_{32}$)?

$$C_{15}H_{32}(l) + 21O_2(g) \rightarrow 12CO_2(g) + 16H_2O(l) + C(s) + 2CO(g)$$

What two criteria determine whether an organic compound will burn with a sootier flame?

Carbon content and carbon-to-hydrogen (C:H) ratio.

Why does $C_6H_{12}$ burn with a sootier flame than $C_3H_6$?

$C_6H_{12}$ has a higher carbon content, leading to a higher chance of incomplete combustion.

Why does $C_3H_6$ burn with a sootier flame than $C_3H_8$?

$C_3H_6$ has a higher carbon-to-hydrogen ratio ($3/6$) than $C_3H_8$ ($3/8$).

What is the definition of cracking in organic chemistry?

A process of breaking down large molecules (long-chain hydrocarbons) into smaller ones by heating at high temperature or using a catalyst.

Why must air be absent during a cracking reaction?

To prevent combustion from occurring.

What mandatory type of organic product must be present in a cracking product mixture?

At least one alkene.

What process is needed to obtain one pure product from a cracking mixture?

Fractional distillation.

What are the temperature and pressure conditions for thermal cracking?

Temperature of $700-750\,^{\circ}\text{C}$ and pressure of $6\,\text{atm}$.

What catalyst is used in thermal cracking?

No catalyst is used in thermal cracking.

What are the temperature and pressure conditions for catalytic cracking?

Temperature of $400-500\,^{\circ}\text{C}$ and pressure of $1\,\text{atm}$.

What catalysts can be used in catalytic cracking?

$Al_2O_3$ or broken pieces of unglazed porcelain ($SiO_2$).

Is cracking an endothermic or exothermic process?

Cracking is an endothermic reaction (absorbs heat from surroundings).

What are two key reasons why cracking is an important industrial process?

1. Breaks large hydrocarbons to produce petrol to meet high demand; 2. Serves as a source of alkenes as raw materials for synthetic products like plastics.

Why are broken pieces of unglazed porcelain used in the experimental set-up for cracking?

Their larger surface area increases the reaction rate.

Why should the catalyst be heated strongly rather than the glass wool soaked with medicinal paraffin during cracking?

To prevent paraffin from vaporizing too quickly and passing through the catalyst without being cracked.

Why is the first test tube of collected gas discarded during a cracking experiment?

It consists mainly of displaced air.

What safety step must be taken when collecting cracking products over water before stopping heat, and why?

Remove the delivery tube from water before turning off heat to prevent water from sucking back and cracking the test tube.

Why is displacement of water used to collect gaseous cracking products?

Because alkanes and alkenes are insoluble in water.

What is the average relative molecular mass (R.M.M.) of air used to compare gas collection methods?

$$28.9$$

What gas collection method is suitable for gases with relative molecular mass greater than air, such as $CO_2$, $Cl_2$, and $SO_2$?

Downward delivery.

What gas collection method is suitable for gases with relative molecular mass less than air, such as $He$, $H_2$, and $NH_3$?

Upward delivery.

What is the definition of a substitution reaction?

A chemical reaction in which an atom (or group of atoms) in a molecule is replaced by another atom (or group of atoms).

What reaction conditions are needed for alkanes to undergo substitution with halogens?

Halogens (e.g., $Cl_2$ or $Br_2$) under UV light (diffuse sunlight) or heat.

What is the function of UV light in the substitution reaction of alkanes with halogens?

UV light provides sufficient energy to break the covalent bond between halogen atoms ($Cl-Cl$ or $Br-Br$).

What solvent is typically used to dissolve halogens in alkane substitution reactions?

An organic solvent, usually $CCl_4$.

What is the expected observation when an alkane reacts with halogen under UV light?

The color of the halogen fades away slowly.

What are the colors of bromine ($Br_2$) in aqueous solution and in organic solvent?

Brown in aqueous solution, and orange in organic solvent.

What is the color of iodine ($I_2$) in organic solvent?

Purple.

What is the reactivity order of halogens down Group 17 in substitution reactions with alkanes?

$$F_2 > Cl_2 > Br_2 > I_2$$

Why does halogenation of alkanes produce a mixture of haloalkane products?

Because the monosubstituted haloalkane undergoes further substitution to form di-, tri-, and tetra-substituted haloalkanes.

How can the yield of monosubstituted haloalkane be maximized during substitution of alkanes?

By using an excess amount of alkane.

What type of haloalkane product is obtained if an excess amount of halogen is used in alkane substitution?

Poly-substituted haloalkanes (di-, tri-, or tetra-substituted).

What are the three sequential steps in the chain mechanism of free radical chlorination of methane?

Step 1: Initiation, Step 2: Propagation, Step 3: Termination.

What is a free radical?

An atom or group of atoms with an unpaired electron that does not obey the octet rule and is highly reactive.

What chemical equation represents the initiation step in the chlorination of methane?

$Cl_2 \rightarrow 2Cl\cdot$ (under UV light)

What chemical equations represent the two propagation steps in the chlorination of methane?

$CH_4 + Cl\cdot \rightarrow \cdot CH_3 + HCl$ and $\cdot CH_3 + Cl_2 \rightarrow CH_3Cl + Cl\cdot$

What general rule describes the reactants and products in every propagation step of free radical substitution?

1 radical + 1 non-radical $\rightarrow$ 1 non-radical + 1 radical.

What chemical equations represent possible termination steps in the chlorination of methane?

$2Cl\cdot \rightarrow Cl_2$, $CH_3\cdot + Cl\cdot \rightarrow CH_3Cl$, and $2CH_3\cdot \rightarrow CH_3CH_3$

How do alkanes behave when tested with bromine in an organic solvent under UV light versus in the dark?

Alkanes decolorize orange bromine under UV light, but show no reaction in the dark environment.

What is the definition of an addition reaction?

A reaction in which two or more molecules react to give a single product.

What functional group conversion occurs during catalytic hydrogenation of alkenes?

Alkene to alkane.

What are the reagents and reaction conditions for catalytic hydrogenation of alkenes?

Hydrogen gas ($H_2$), finely divided $Pt$, $Pd$, or $Ni$ catalyst, at room temperature.

What is catalytic hydrogenation used for in the food industry, and what undesirable byproduct can be formed?

Used to convert liquid animal/vegetable oils into margarine; produces trans fats.

What functional group conversion occurs during halogenation of alkenes?

Alkene to dihaloalkane.

What reaction conditions are necessary to synthesize pure dihaloalkanes from alkenes via halogenation?

Halogen dissolved in organic solvent (usually $CCl_4$) without UV light (in the dark).

Why is bromine water ($Br_2(aq)$) not used if pure dihaloalkanes are desired from alkenes?

Water causes the formation of side products.

What reaction conditions are required for the hydrohalogenation of alkenes?

Hydrogen halide ($HX$) under room conditions, usually as a gas, never in aqueous solution.

State Markovnikov's rule for the addition of hydrogen halides to asymmetric alkenes.

The major product is the one where the hydrogen atom is added to the carbon atom of the C=C bond that already carries a larger number of hydrogen atoms.

How many products are obtained when a hydrogen halide reacts with a symmetric alkene?

Only one product is formed.

What functional group conversion occurs during the reaction of alkenes with cold, dilute potassium permanganate?

Alkene to diol (dihydroxylation).

What conditions are required to synthesize a pure diol from an alkene using potassium permanganate?

Cold, dilute acidic or alkaline $KMnO_4(aq)$.

What are the expected observations when an alkene reacts with cold, dilute alkaline $KMnO_4(aq)$?

Purple $KMnO_4(aq)$ fades away (turns colourless) and a brown precipitate ($MnO_2$) forms.

What are the expected observations when an alkene reacts with cold, dilute acidified $KMnO_4(aq)$?

Purple $KMnO_4(aq)$ fades away (turns colourless).

Why should hot, concentrated $KMnO_4(aq)$ not be used if diol synthesis from an alkene is intended?

It further oxidizes the diol to a ketone or dioic acid, resulting in a low yield of diol.

Why is there no reaction between an alkene and acidified potassium dichromate ($K_2Cr_2O_7/H^+$)?

Because the oxidizing power of acidified potassium dichromate is not strong enough.

How can bromine dissolved in organic solvent be used to distinguish an alkene from an alkane in the dark?

The alkene decolorizes orange bromine in the dark, whereas the alkane shows no reaction.

What functional group conversion occurs during substitution of haloalkanes with hydroxide ions?

Haloalkane to alcohol.

What reagents and reaction conditions are required for the substitution of haloalkanes with hydroxide ions?

$NaOH(aq)$ or $KOH(aq)$, heating under reflux.

What are two purposes of heating under reflux during the conversion of haloalkanes to alcohols?

1. Speeds up the rate of reaction; 2. Prevents the loss of volatile organic substances (such as alcohols).

Why is a water bath used instead of direct heating when refluxing organic reaction mixtures containing haloalkanes/alcohols?

Because organic compounds like alcohols are flammable.

Describe the two-step procedure to test for the halogen substituent in a haloalkane ($R-X$).

Step 1: Warm haloalkane with $NaOH(aq)$; Step 2: Cool, add excess dilute nitric acid, and then add silver nitrate solution ($AgNO_3(aq)$).

What precipitate color is observed in the silver nitrate test for chloro-, bromo-, and iodoalkanes?

White precipitate for $R-Cl$, pale yellow precipitate for $R-Br$, and yellow precipitate for $R-I$.

Why is direct treatment of haloalkanes with silver nitrate solution ($AgNO_3(aq)$) ineffective?

Haloalkanes do not contain free halide ions ($X^-$).

Why cannot halogen atoms attached directly to a benzene ring undergo substitution with $OH^-(aq)$?

Because the benzene ring is very stable.

What is the definition of a primary ($1^{\circ}$) alcohol?

An alcohol with one alkyl group attached to the carbon atom bearing the -OH group.

What is the definition of a secondary ($2^{\circ}$) alcohol?

An alcohol with two alkyl groups attached to the carbon atom bearing the -OH group.

What is the definition of a tertiary ($3^{\circ}$) alcohol?

An alcohol with three alkyl groups attached to the carbon atom bearing the -OH group.

What is the order of reactivity among primary, secondary, and tertiary alcohols?

Tertiary ($3^{\circ}$) > Secondary ($2^{\circ}$) > Primary ($1^{\circ}$).

What two common methods convert alcohols to haloalkanes via substitution?

Method 1: Using hydrogen halides ($HX$); Method 2: Using phosphorus trihalides ($PX_3$).

What functional group conversion occurs during dehydration of alcohols, and what type of reaction is it?

Alcohol to alkene; it is an elimination reaction.

What is the definition of an elimination reaction?

A reaction in which a small molecule is removed from a reactant.

What role does concentrated $H_2SO_4(l)$ play in the dehydration of alcohols under heating?

Concentrated $H_2SO_4(l)$ acts as a dehydrating agent (not a catalyst).

What role does $Al_2O_3(s)$ play in the dehydration of alcohols under heating?

$Al_2O_3(s)$ acts as a catalyst (not a dehydrating agent).

State Zaitsev's rule for predicting the major product in alcohol dehydration.

The major product is the more substituted alkene (having a larger number of alkyl groups attached to C=C).

What organic products are formed when primary, secondary, and tertiary alcohols undergo oxidation?

Primary alcohol yields aldehyde then alkanoic acid; secondary alcohol yields ketone; tertiary alcohol gives no reaction.

How is mild oxidation of a primary alcohol to an aldehyde achieved experimentally?

Add dilute acidified $K_2Cr_2O_7(aq)$ dropwise to excess primary alcohol, heat under reflux, and immediately distill out the aldehyde.

Why cannot dilute acidified $KMnO_4(aq)$ be used for mild oxidation of a primary alcohol to an aldehyde?

Its oxidizing power is too strong, converting primary alcohol directly to alkanoic acid.

What color change occurs when acidified $K_2Cr_2O_7(aq)$ oxidizes primary or secondary alcohols?

Orange ($Cr_2O_7^{2-}(aq)$) turns to green ($Cr^{3+}(aq)$).

How is the oxidation of alcohol by acidified potassium dichromate applied in law enforcement breathalyzers?

It detects alcohol content in breath samples of suspected drunken drivers by changing color from orange to green.

What are the reagents and expected observation in the esterification test for alkanols?

React alkanol with carboxylic acid in the presence of conc. $H_2SO_4(l)$; forms an ester with a sweet fruity smell and two immiscible layers.

What reagent and condition are required to reduce a carboxylic acid directly to a primary alcohol?

Step 1: Lithium aluminium hydride ($LiAlH_4$) in dry ether; Step 2: Acid ($H^+(aq)$).

Why must lithium aluminium hydride ($LiAlH_4$) be used in dry ether rather than in aqueous solvent?

$LiAlH_4$ reacts vigorously with water.

Why is sodium borohydride ($NaBH_4$) described as a selective reducing agent compared to $LiAlH_4$?

$NaBH_4$ can be used in water directly and selectively reduces aldehydes and ketones to alcohols, but cannot reduce carboxylic acids.

How can an aldehyde be distinguished from a ketone using acidified potassium dichromate solution?

Aldehyde turns acidified $K_2Cr_2O_7(aq)$ from orange to green, whereas ketone shows no color change.

What dual functions does concentrated $H_2SO_4(l)$ perform in an esterification reaction?

Concentrated $H_2SO_4(l)$ acts as both catalyst and dehydrating agent (removing water to shift equilibrium to the right).

What are two methods for converting a carboxylic acid into an amide?

Method 1: Mix with $PCl_3$, then $NH_3$; Method 2: Mix with $NH_3$ and heat ($\Delta$).

What is the main operational and product-yield difference between acidic and alkaline hydrolysis of esters?

Acidic hydrolysis uses acid as a catalyst, is reversible, and gives a low yield; Alkaline hydrolysis uses alkali as a reactant (followed by acid), is irreversible, and gives a higher yield.

How can an unsubstituted amide be distinguished from a substituted amide or amine?

Heat with alkali ($NaOH(aq)$) under reflux; unsubstituted amide yields ammonia gas ($NH_3$) with a pungent smell, whereas substituted amides do not.