It refers to the instability of oxides of bromine as compared to relative stability of oxides of chlorine and Iodine at room temperature, the former being stable only at low temperatures.

The dramatic differences between the properties of molecules formed from the late p-block elements of the first row of the periodic table (N–F) and those of the corresponding elements in subsequent rows is well recognized as the first row anomaly.

The second period contains the elements lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon. In a quantum mechanical description of atomic structure, this period corresponds to the filling of the second (n = 2) shell, more specifically its 2s and 2p subshells.

Bromine-Oxygen bonds in its higher oxides are least stable among other Halogen-Oxides, because it lacks both: Higher polarity as in the case of iodine and multiple bond formation involving the d-orbitals as in the case of Chlorine.

Bromine has 4 shells, whereas iodine has 5. Positively charged protons are found in the nucleus of the atom. For bromine or iodine to react, each atom needs to gain an electron to fill up its shell so that it is in a more stable state.

The cause behind the middle row anomaly is because all 10 electrons in the bromine atom’s third orbital that is 3d are comparatively close to the nuclear and exert comparatively less repulsion on the five electrons in its fourth orbital 4p.

Iodine-Oxygen bond will be more stable in case of higher oxides because of higher polarity (2.5 vs 3.5) and also because more electrons are available (more atoms=more electrons) for sharing (covalent bond= satisfying hunger for electrons through sharing).

The pair of electrons in valence s-orbital is reluctant to take part in bond formation due to poor shielding effect of −d and f-electron in heavier elements. It is called inert pair effect due to which lower oxidation state becomes more stable than higher oxidation state in case of p-block elements.

The inert-pair effect is the tendency of the two electrons in the outermost atomic s-orbital to remain unshared in compounds of post-transition metals. The term “inert pair” was first proposed by Nevil Sidgwick in 1927.

Poor shielding means poor screening of nuclear charge. In other words, the nuclear charge is not effectively screened by electrons in question. The shielding effect of different orbitals is as follows:​ s orbital’s > p orbital’s> d orbital’s> f orbital’s.

-Inert pair effect is a result of poor shielding of d and f orbitals and filling of electrons in Al does not involve any d or f orbital. Thus, Al cannot be the correct answer.

The inert pair effect is shown by Tl, Pb and Bi due to which, the lower oxidation state is more stable than the higher oxidation state. But C, being higher up in the periodic table, does not show inert pair effect.

Hence, due to small size and absence of d and f orbitals, Aluminium does not show inert pair effect.

Due to this the nucleus tightly holds the outermost electrons. This decreases the electropositive character. Hence, the correct answer is the option (D) B < Al > Ga > In > Tl.

Ketones. There is no E-effect in ethers .

+R effect: The +R effect or positive resonance effect is expressed by the electron donating groups (for eg. –NO2, -COOH etc) which withdrwas electrons from the rest of the molecule by delocalization of electrons within the molecule. It results into decrease in the electron density on the rest of the molecule.

Oxygen is much more electronegative than carbon so it can withdraw electron density by the inductive effect. However, it is very important to note that OH is NOT an electron withdrawing group. It is an electron DONATING group.

Yes, OCH3 which belongs to the is the electron-withdrawing group (methoxy group). Here, the oxygen (in OCH3) is more electronegative than carbon due to which it will show -I effect which is electron-withdrawing.

Electron withdrawing groups (EWG) with π bonds to electronegative atoms (e.g. – C=O, -NO2) adjacent to the π system deactivate the aromatic ring by decreasing the electron density on the ring through a resonance withdrawing effect.

An electron withdrawing group (EWG) is a group that reduces electron density in a molecule through the carbon atom it is bonded to….The strongest EWGs are groups with pi bonds to electronegative atoms:

• Nitro groups (-NO2)
• Aldehydes (-CHO)
• Ketones (-C=OR)
• Cyano groups (-CN)
• Carboxylic acid (-COOH)
• Esters (-COOR)

Electron withdrawing groups have an atom with a slight positive or full positive charge directly attached to a benzene ring. Examples of electron withdrawing groups: -CF3, -COOH, -CN. Electron withdrawing groups only have one major product, the second substituent adds in the meta position.

Aromatic amines have the nitrogen atom directly connected to an aromatic ring structure. Due to its electron withdrawing properties, the aromatic ring greatly decreases the basicity of the amine – and this effect can be either strengthened or offset depending on what substituents are on the ring and on the nitrogen.

Aromatic amines are weaker bases than aliphatic amines. This is because the amine donates its electron density to the aromatic ring. Electron withdrawing groups on the aromatic amine decrease the basicity of aromatic amines. This is because the electron withdrawing groups steal electron density from the nitrogen.

For example, an oxygen atom in a hydroxy group (OH) is electron withdrawing by induction, but electron donating by resonance when placed in a position on the structure where resonance is possible This will be explained more fully below.

Numerous studies on nitro group properties are associated with its high electron-withdrawing ability, by means of both resonance and inductive effect.

Atoms with pi-bonds to electronegative groups – Strongly deactivating. NO2, CN, SO3H, CHO, COR, COOH, COOR, CONH2. All pi-acceptors. Electron withdrawing groups with no pi bonds or lone pairs – Strongly deactivating.

Why is -OCH3 more strongly activating than -CH3 in electrophilic aromatic substitution? Facts I know: 1) More the electron density in benzene ring, the faster the reaction. 2) Lone pair on -OCH3 group undergoes resonance and makes ortho-para positions electron rich, and so does -CH3 by hyperconjugation.

Some common ortho para directing groups are –Cl, -Br, -I, -OH, -NH2, -CH3, -C2H5. The group which directs the second incoming group to the meta position, is called a meta-director. For example, alkylation of nitro benzene gives m-alkylnitro benzene as major product.