S3.2 Functional groups: HL Part 1

Question 1

What causes cis-trans isomerism in molecules?

Answer 1

Cis-trans isomerism is caused by restricted rotation around a double bond (C=C) or within a ring structure, requiring two different atoms or groups attached to each carbon of the C=C bond or positions around the ring.

Question 3

How to identify cis-trans isomerism in non-cyclic alkenes?

Answer 3

Identify a C=C bond with different atoms or groups on each carbon. Cis isomers have similar groups on the same side, while trans isomers have them on opposite sides.

Question 4

How to recognize cis-trans isomerism in C3 and C4 cycloalkanes?

Answer 4

Observe substituents’ arrangement around the ring. In cis isomers, substituents are on the same side of the ring plane; in trans isomers, they are on opposite sides.

Question 5

How do you depict a tetrahedral arrangement around a chiral carbon in stereochemical formulas?

Answer 5

Place the chiral carbon at the center. Use solid tapered bonds for groups pointing towards the viewer and dashed tapered bonds for groups pointing away. Solid lines represent groups in the same plane as the paper or screen.

Question 6

What is the significance of a chiral carbon atom in the formation of stereoisomers?

Answer 6

A chiral carbon atom, bonded to four different atoms or groups, leads to stereoisomers known as enantiomers. These are non-superimposable mirror images of each other, with distinct optical properties, rotating plane-polarized light in opposite directions.

Question 7

How are enantiomers recognized in 3D modeling?

Answer 7

Enantiomers are non-superimposable mirror images, similar to left and right hands. They are recognized by mirroring the arrangement of substituents around the chiral carbon while maintaining the tetrahedral geometry.

Question 8

How do you determine the molar mass of a compound using MS?

Answer 8

Identify the molecular ion peak in the mass spectrum, which indicates the molar mass of the compound.

Question 9

What is the significance of analyzing fragmentation patterns in MS?

Answer 9

It allows for the identification of smaller fragments, shedding light on the structure of the compound by comparing fragment masses to the molecular ion’s mass.

Question 10

How can you deduce the mass of neutral fragments lost during MS fragmentation?

Answer 10

By comparing the mass of the fragments to the original molecular ion’s mass and using data tables for possible neutral fragment mass losses.

Question 11

How do fragmentation patterns help infer structural features of a compound?

Answer 11

Fragmentation patterns, alongside data on neutral fragment losses, aid in deducing features like specific functional groups or chain lengths.

Question 12

Infrared spectroscopy

Answer 12

An analytical technique that uses IR radiation to determine the type of bonds present in an organic compound.

Question 13

Modes of vibration

Answer 13

The different ways that a bond can bend or stretch when exposed to IR radiation.

Question 14

What wavenumber range and intensity characterizes C—I bonds in IR spectroscopy?

Answer 14

490–620 cm−1, Strong intensity.

Question 15

What wavenumber range and intensity indicates the presence of C—Br bonds in IR spectroscopy?

Answer 15

500–600 cm−1, Strong intensity.

Question 16

Describe the wavenumber range and intensity for C—Cl bonds according to IR spectroscopy.

Answer 16

600–800 cm−1, Strong intensity.

Question 17

At what wavenumber range are C—F bonds found in IR spectroscopy, and what is their intensity?

Answer 17

1000–1400 cm−1, Strong intensity.

Question 18

For IR spectroscopy, what wavenumber range and intensity are characteristic of C—O bonds?

Answer 18

1050–1410 cm−1, Strong intensity.

Question 19

What does a wavenumber range of 1620–1680 cm−1 with medium-weak intensity suggest in IR spectroscopy?

Answer 19

Presence of C=C bonds (Alkenes) with multiple bands.

Question 20

In IR spectroscopy, how are C=O bonds identified in terms of wavenumber and intensity?

Answer 20

1700–1750 cm−1, Strong intensity.

Question 21

What wavenumber range and intensity are associated with C≡C bonds in IR spectroscopy?

Answer 21

2100–2260 cm−1, Variable intensity.

Question 22

How are O—H bonds in carboxylic acids identified in IR spectroscopy, and what is their characteristic intensity?

Answer 22

2500–3000 cm−1, Strong, very broad.

Question 23

Describe the wavenumber range and intensity for O—H bonds in alcohols and phenols as per IR spectroscopy.

Answer 23

3200–3600 cm−1, Strong, broad.

Question 24

What wavenumber range and intensity indicate the presence of N—H bonds in primary amines according to IR spectroscopy?

Answer 24

3300–3500 cm−1, Medium intensity with two bands.

Question 25

The two main regions of an infrared spectrum

Answer 25

Fingerprint region and the functional group region

Question 26

IR active

Answer 26

A gas (known as a greenhouse gas) that can absorb IR radiation by undergoing a change in its dipole moment.

Question 27

IR inactive

Answer 27

A gas that does not absorb IR radiation.

Question 28

Functional group region

Answer 28

The region of an IR spectrum that can be used to determine the bonds (and their functional groups) present in an IR spectrum.

Question 29

The region of an IR spectrum that can be used to determine the identity of an organic compound.

Answer 29

Fingerprint region