10. Organic Chemistry Flashcards

Question

_{(Alkane Reactions)} Substitution Reactions Methane + Br₂

Answer 1

* Br₂ undergoes homolytic fission * 1 Br molecule joines with an H molecule which breaks away from CH₄ CH₄ + Br₂ --_^(UV)--\> CH₃Br + HBr

Answer 2

* **sp² hybridized at 120 degrees with an outer π bond** that is the **site of reactivity** allowing range of addition reactions * bonds in C=C are not as stable as single bonds --\> **energetically favorable to be converted to single bonds** * they have a high electron density making their activation energy low

Answer 3

* HX + Alkene --\> Halogenoalkane * Halogen + Alkene --\> Halogenoalkane * Water + Alkene --\> Alcohol * Polymerization

Answer 4

C₂H₅OH_(l) + 3O₂_(g) --\> 2CO_2(g) + 3H₂O_(l) * Extreme form of oxidation * Produces CO₂ + H₂O * **Burns more cleanly than their equivalent alkanes** * O in the compound is available for combustion products so less CO made in limited O₂ conditions * Alcohols with longer chains have greater molar enthalpies, but may not be able to burn cleanly * **Energy released increases down functional group**

Answer 5

_Tertiary Alcohol_ * C₄OH --\> **not easily oxidized** (resistant to normal oxidation) _Secondary Alcohol_ * C₃HOH --\> **ketone** C₃O --\> no further oxidation _Primary Alcohol_ * C₂H₂OH --\> **aldehyde** C₂OH --\> **c****arboxylic acid** C₂OOH

Answer 6

* Alcohol is dripped into a warm solution of acidified **KMnO₄** / **K₂Cr₂O₇** * K₂Cr₂O₇ is reduced from orange to green * Cr(IV) --\> Cr(III) * Aldehydes have low boiling points (no H bonding) ==\> **distill** before being oxidized further * **Reflux** the mixture to produce acid * condense back into mixture from aldehyde ==\> oxidized to acid

Answer 7

CH₃CHOHCH₃ + [O] --\> CH₃COCH₃ + H₂O ^{propan-2-ol KMnO₄ / K₂Cr₂O₇ Propanone} * Alcohol is **refluxed with acidified K₂Cr₂O₇ --\> ketone** * on prolonged treatment with a powerful oxidizing agent they can be further oxidised to a mixture of acids with fewer C atoms than the original alcohol

Answer 8

Carboxylic Acid + Alcohol \<---\> Ester + Water

Answer 9

Reactants with a non-binding pair of electrons that are attracted to a positive carbon (a form of electrophile)

Answer 10

* Halogenoalkanes are reactive and undergo nucleophilic substitution reactions from nucleophile attack R-X_(l) + OH^-_(aq) --\> R-OH_(aq) + X^-_(aq) with NaOH: CH₃CH(Cl)CH₂CH₃ + NaOH --\> CH₃CH=CHCH₃ + NaCl + H₂O conditions: heat (boil)

Answer 11

Nitration of Benzene * Firstly sulfuric acid is stronger so it protonates the nitric acid * with heat the electrophilic substitution by the nitronium ion causes a momentary loss of symmetry of the electron structure of benzene

Answer 12

* The oxidation of alcohols can be reversed by reduction CH₃COOH --^_[H+]--\> 3CH₃CHO --^_[H+]--\> CH₃CH₂OH ^{carboxylic acid aldehyde primary alcohol} * Needs lithium aluminium hydride LiAlH₄ in dry ether (CH₃)₂CO --^_[H+]--\> (CH₃)₂CHOH ^{Ketone Secondary Alcohol} * Needs heat with sodium borohydride NaBH₄

Answer 13

A series of discrete chemical steps to change a reactant to a desired product

Answer 14

Configurational * **can be interconverted only by breaking bonds** Conformational * can be interconverted by free roation about σ bonds

Answer 15

* _Cis isomers are those with the same groups on the same side_ of the double bond or cyclical compounds * _Trans isomers have the groups on the opposite sides_ of the double bond

Answer 16

* Isomers with more than 2 different groups, the group with the highest priority on the left hand side is determined, and then that of the right * E Isomers - have these two groups opposite * Z Isomers - have these two groups on the same side * Priority rules * the atom w/ highest atomic number * if atom the same, apply rule to next bonded atom in chain

Answer 17

Cis * Inductive effect leads to polarity --\> higher b.p. * Limited/reduced intermolecular bonding --\> lower b.p. Trans * Inductive effects balance --\> lower b.p. * Extensive intermolecular bonding --\> higher b.p.

Answer 18

* _non-superimposable on each other_ * exists in pairs - **enantiomers** * diastereomers contain two or more chiral carbons --\> not mirror images

Answer 19

* Isomers differ in their reaction to plane-polarised light * plane polarised light vibrates in one direction only * one isomer rotates light to the right, the other to the left * reotation measured by polarimeter * if light appeares to have * turned to the **right --\> Dextrorotatory (d / +)** * turned to the **left --\> Laevorotatory (l / -)**

Answer 20

A 50-50 mixture of the two enantiomers (dl) or (+-) * the opposite optical effects of each isomer cancel each other out

Answer 21

* Light source produces light vibrating in all directions * polarising filter only allows through light vibrating in one direction * plane polarised light passes through sample * if substance is optically active it rotates the plane polarised light * analysing filter is turned so that light reaches a maximum * direction of rotation is measured coming towards the observer

Answer 22

* _Formation of racemic mixtures is more likely in a lab reaction_ than in a chemical process occuring naturally in the body * if a compound can exist in one form, only one of the optical isomers is usually effective * _the separation of isomers will make manufacturing more expensive_ * a drug made up of both isomers will require a larger dose --\> may cause problems if the other isomer is 'poisonous' - a **tetratogen**

Answer 23

Polar * Have dipole moments due to different electronegativities (solvents must be polar or won't react with H2O) Non-polar * Similar electronegativities

Answer 24

Protic * **Polar solvents with OH/ NH bonds allowing hydrogen bonding** and **a source of protons**_{(eg water/ ethanol)} Aprotic * A polar / non-polar solvent that do not have OH/ NH bonds nor provide a source of protons_{(eg acetone, benzene, hexane)}

Answer 25

The hydrogren will attach to the carbon that is already bonded to the greater number of hydrogens

Answer 26

* Involve heterolytic fission + nucleophilic substituion **with primary haolgenoalkane** * _unstable transition state created_ --\> bimolecular * Rate = k[halogenoalkane][nucleophile] * **Polar Aprotic Solvents preferred** - unable to form H bonds (or solvent would bind to nucleophile inhibiting its action)

Answer 27

* Involve heterolytic fission + nucleophile substitution with **tertiary halogenoalkane** * **Steric hindrance** - halogen must be heterolytically removed to create a carbocation before nucleophile can be attached * _creates more stable intermediate_ --\> reaction is unimolecular * **Polar protic solvents preferred** -form H bonds which stabilize the carbocation by ion-diple interactions

Answer 28

* Stabilization of a carbocation because the other alkyl groups can unevenly share their electrons with the positive centered carbon

Answer 29

Carbocation intermediate

Answer 30

Unstable transition state

Answer 31

* As halogen-carbon bonds become less polar, it would be expected that the nucleophilic attack to be less and so rate decreases down the group * F \> Cl \> Br \> I * In reality: _energy to break bonds must be considered_ * **C-I \> C-Br \> C-Cl \> C-F**

Answer 32

* In general **S_N1 tertiary reaction rates are faster than S_N2 primary due to the stability of the formation of carbocations** Tertiary \> Secondary \> Primary ^{S_N1 S_N1 & S_N2 S_N2}

10. Organic Chemistry Flashcards

(61 cards)