Treatment of 2,4,6-tri-tert-butylphenol with bromine in cold acetic acid gives the compound c18h29bro in quantitative yield. the infrared spectrum of this compound contains absorptions at 1630 and 1655 cm^-1. its 1h nmr spectrum shows only three peaks (all singlets), at δ 1.2, 1.3, and 6.9, in the ratio 9: 18: 2. what is a reasonable structure for the compound?

2,4,6-tri-tert-butylcyclohexa-2,5-dienone

Explanation:

1. Information from the formulas

C₁₈H₃₀O ⟶ C₁₈H₂₉BrO

A Br has replaced an H.

2. Information from the reaction

These look like the conditions for an electrophilic aromatic substitution.

3. Possible mechanism (Fig. 1)

The product must be highly symmetrical, because there are so few NMR signals.

(i) The bromonium ion attacks at the para position, forming a resonance-stabilized carbocation intermediate.

(ii) A bromide ion attacks the H of the hydroxyl group to form 2,4,6-tri-tert-butylcyclohexa-2,5-dienone.

4. Confirmatory evidence (Fig. 2)

(a) Infrared  

1630 cm⁻¹:  C=O stretch

1655 cm⁻¹ : C=C stretch

(b)NMR

1.2 (9h, s):    the 4-tert-butyl group

1.3 (18H, s): the 2- and 6- tert- butyl groups

6.9 (2H, s):    the alkene H atoms

The ratio is 9:18:2.

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms